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how to make your 300 quieter from road noise

29K views 51 replies 16 participants last post by  CtCarl 
#1 · (Edited)
I have quietened down my 300 from tire noise a noticeable amount. Most of this comes from the rear and enters the car through the parcel shelf and is fairly easy to attenuate. This will impact the sound of your stereo which can be a good thing or bad depending on your preference. If you fold down the rear seats, you will see some upholstery bolsters that are beside the rear seat, also take out the trunk floor. There is 1 bolt and a clip near the top if you grab the bolster and pull a plastic clip will release allowing you to take out the bolsters. If you look near the top you will see a spring clip and the plastic clip, pull the clip out and attach it back to the bolster with the plastic clip, then when you go to re install it just pop the steel clip back in place and put the bolt back in. Now on to making it quieter you will see 2 plastic push clips that hold the vertical trunk liner where you took out the seat bolster pop these out and push the trunk liner to one side and you will see the rear wheel well also reach around the corner and there is a black plastic bag with the factories effort at noise abatement, take this out now get either dacron fill from a craft store I used almost 2 20 ounce bags of the dacron fill or possibly Walmart, rock wool house insulation or even fiberglass insulation but it itches badly when you go to install it. There are also 2 plastic clips holding the parcel shelf closeout panel pull these out you will need a trim tool as they are really in there, now you are ready to pack the insulation in the parcel shelf area, in the cavity over the wheel well, and behind the rear seat trim bolster area. Reinstall every thing you will now have a quieter car. As to the stereo in mine which is an S model which has the beats sub woofer the base losses a lot of the boominess sound which I personally prefer you will have to adjust you eq. A cheap and simple mod also watch out for the velcro strips and the insulation it tends to grab onto it. On mine I changed the Firestones to Hankook V2 which are a lot quieter and then did the insulation trick and mine is quieter yet again so I would think if you are on 20" Firestones it will really be noticeable.
 
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#4 ·
I did about 3x as much as Maddog did in his car, but I wasn't concerned with road noise. I did it to stop the rattling from my 136 dB sound system. A side benefit is it lowered road noise from the tires, etc.

Seriously though, you did the trunk as Maddog shows in his pics, plus did the same in the cabin, you wouldn't need to do much of anything else. Front and rear road noise would be reduced.
 
#6 ·
I don't know what Maddog used (it looks like Peel & Seal), but I used a combination of dynamat for the first layer, then 3 layers of edead, followed by a layer of ensolite.

The company that made edead is no longer in operation though. It was really good stuff, and probably the most cost effective.
 
#7 ·
Soundqubed makes great sound dampener. Its called Q-mat. All of us guys on stevemeade forum were testing fatmat, dynamat, secondskin, etc. Secondskin is the best out there but expensive. For the price Q-mat is the cheapest and close to the most effective (secondskin). Back when i had my grand marquis i was about a decibel off from 150. Took out the old sound dampener and replaced with Q-mat and i made it into the 150db group.

Road noise was way down, midbass from the doors was dramatically improved as we sealed off the doors with the sound dampener.

I really recommend Q-mat to anyone.
 
#9 ·
So Maddog didn't use Peel & Seal. IMO what he used is a much better product. RAMMAT is a great deadener. RAAMaudio also sells the ensolite I mentioned. That would be a serious combo if the two were used together.
 
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#11 ·
Well, I have to lift my trunk lid as it wouldn't go up by itself. It wasn't so heavy that it wouldn't stay up, but it was too heavy to go up when I opened it.

But it was dead silent when I played my music at loud levels.
 
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#21 ·
Same here but that's because I have the gas struts instead of springs. If you have the springs then its easy to have the boot lid (trunk) open by itself instead as Kaiser Bill said opens a bit then needs manual intervention.

I am still working on a way to do this as well as Auto rear windows, auto shut of windows and roof, auto door mirrors on locking of car. After I have sorted the auto box issues :-(
 
#24 · (Edited)
Mine opened until I deadened it to the point you could even tell it was released when I hit the button.

Before I added the sound deadening, it would open.

I didn't expect to have an automatically opening trunk lid, such as a power assist option. But I can say it did open when I hit the button.

Again, I had no expection for this to continue when I added the mass as I was trying to quiet the car.

If your trunk lid doesn't move when you hit the release, the struts may need to be looked at.
 
#25 · (Edited)
When I got my 300, I applied GTMAT (that I had bought from eBay) all over the trunk bottom and sides. Honestly, I did that just because it was easy access, and lots of bare metal to cover!

The real problem is that a lot of road noise seems to be from the front! I did apply as much GTMAT as I could in the passenger side -- the plastic panel at the sill pops off easily and then the right-side kick panel pops off easily, then the carpet can be elevated a bit. It's tough without removing more panels. I could only go partway up the firewall.

I'm not sure that it had much effect. I'll do the driver's side, even though I'm not sure how much it's helping. It seems there's so much road noise coming up through the front struts that it's going to be hard to reduce.

Perhaps a tire change from the factory set will end up being the best thing for reduced noise. I know on a number of trucks/suv's I've owned, swapping out the factory Michelins and Wranglers to BFG Long Trail T/A's has cut tire noise enormously.
 
#26 ·
You are correct a lot of road noise does come from the front. I put a front strut brace in mine and it had a noticeable change in pitch of the sound coming into the cabin. Also another clue is the factory went to the trouble of putting sound deadner panels on the underside of the car which leads me to believe a lot of the noise does come through the floor pan. I have lined the trunk and the doors with Frost King which is a stick on duct liner similar to Dynamat but thicker, not as high a density material but it worked very well cut the road noise a lot. Also stuffed the parcel shelf around the speakers and the trunk closeout panels on each side with dacron stuffing, kind you get at a craft store and it also helped a lot. Need to take out the seats and do under the carpets with the Frost King and will be investigating the front inner fender well areas to see what can be deadened down there. Tires do play a big roll in this I have gone to Hankook V2 as mine has 20" wheels they are a lot better for noise and harshness went up 1 size to a 255 and run them at 30psi. 18" tires with the taller sidewall would be a big improvement as well just I like the look of 20" wheels so its a compromise. Mine is good now on smooth pavement if I am on badly worn pavement it is still too loud for a so called luxury car, I will make mine quieter yet.
 
#27 ·
A strut brace sounds like a great way to reduce their ability to vibrate independently.

Maybe removing a wheel and the fender liner to get access to the suspension area might provide access to any bare metal around the struts where some GTMAT/Dynamat type stuff can be applied ....

From what I've read, one of the biggest things we're doing with the Dynamat type stuff is just adding mass, lowering the ability of the mass to respond to vibrations.
 
#28 ·
got busy today and insulated the front fender wells, the stock noise isolator from Chrysler that goes between the fender and the cowl to stop noise being radiated into the front edge of the door and then into the cabin is an absolute joke. That should be a 1" to 2" think closed cell neoprene seal I have enclosed a picture of the stock piece of STYROFOAM and they where not even installed properly on mine. I have insulated the area on the inner fender panel also the inside of the front fender with Frost King self adhesive foil backed, Dynamat or other will also do and then packed the area from the door seal to the inner fender panel with Dacron insulation, you can get it at a craft store or Walmart could also use rock wool sound insulation. This has had a large effect on road noise coming from the front, the only part of my car I have not done yet is underneath the carpeting, guess I need to do that as well with the Frost King stuff. Finally my car is getting into the area of a luxury car for noise.
 

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#33 · (Edited)
I'm trying to follow your same steps but I'm totally confused about this part... Are those pics taken from outside the vehicle ? are they the covers of the wheels space of the car?

Sorry it's so confusing!

I did the part of the trunk as you described (mine also had the black plastic bag!) and noise got reduced a lot more than I expected!

Also, do you have any guide on how to unmount the front seats?

I'm gonna order the Lexus part you discovered (amazing idea btw).

Thank you for sharing all this information!!
 
#29 · (Edited)
Finished installing noise stop material today, took out the front seats and put the Frost King on the floor boards front and rear. Total comes to 11 rolls of Frost King self stick material so that makes 165 sq.ft. plus four 20oz bags of dacron stuffing 2 bags for the trunk and parcel shelf and 2 bags for the front fender cowl joint and my car is finally in the whelm of a luxury car as far as noise goes, now I am happy with the noise part as a bonus it helps the stereo a lot. Another curios thing is the molded carpet on the passenger side has a lot more noise stop material on the bottom than the drivers side, probably to get more leg room on the drivers side. Also for those who care the drivers side dead rest pedal is a separate piece of plastic that comes off could be modified or removed if need be although the carpet is molded to accommodate the foot rest so you would have to deal with that.
 
#32 · (Edited)
Put on the last of the noise treatment material tonight, it is a pair of secondary door seals from a 2011 Lexus gs350 cost about $18.00 ea and fill in the gap between the front door and the front edge of the rear door these are one of the things that make a Lexus quiet. Measured 78db on a sound meter app on my phone sitting in the cup holders and doing 140km/85mph on the highway on a good road goes up 3db on rougher pavement or bridge decks for example, this is with 1/2 worn 20" Hankook v2 would be quieter still with new rubber. Now Iam happy with the noise level and would now call it a luxury car. It has come miles from where I started in terms of noise. Have one last change to make next week, a new pair of front struts which I am pretty sure will be quieter in the front end again due to the struts being a bit softer than the current ones so they will transmit less road noise into the front cowl area.
 

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#34 ·
We can't believe how quiet the 2015 Platinum C is! Accoustic glass and lots of sound insulation. They've done a bang up job on that. It's a lot quieter than our 2006 Heritage Edition, and I thought that was pretty good!
 
#37 ·
They made a lot of changes to make the gen 2 quieter. One of the major changes is to the glass, but they've also changed the internal door panels quite a bit. A lot of areas where plastic or other materials may rub together they've addressed by adding felt or wrapping wires in non vibrating materials that I didn't see in my gen 1. I laid 3 layers of dampening material and closed cell foam in my cool V. I've only added some foam to certain parts of the door in my gen 2 where the wire wraps to keep things from buzzing had come loose. The one area they missed completely is the rear deck cover. The back edge of this can vibrate against the rear window, especially if you got the H/K system. I had to add a strip of foam along the edge of this.
The rear deck could also use additional deadening as well.

I've only disassembled certain parts of the car, but I can see a lot of focus of noise reduction. There are still some areas to address, but I feel like it is good enough from the assembly line.
 
#41 · (Edited)
On the extra door seals if you have a white car like mine you may just want to use window weather stripping from the home improvement center as the Lexus black seals are not any quieter than my initial test which was with black weather stripping foam from Home Depot as it is available in white as well. On any dark color car the Lexus seals look fine. Also use the the same window weather stripping on the rear doors as well there is no Lexus equivalent part on the rear door. On the rear doors I am using 2 layers of 1/8" x 3/8" as it does not come in 1/4" x 3/8" could probably also use 1/4" x 1/2" instead to make a neater job.
 
#45 ·
I'm gonna install the ones I bought in the same position as you did, also trimming the upper part and will post a picture of it, because my door looks very different from yours .

Thank you for sharing your ideas , it's okay it doesn't cover the whole edge of the door , I mean it's an experiment to isolate the wind noise and it's brilliant !


Sent from AutoGuide.com Free App
 
#46 ·
Also I may not have made it clear the seals go on the front edge of the rear door not the the front door. The front door rear edge closes against the seal mounted on to the rear door, there is a fold in the rear door front edge the seal sticks to and on my gen 2 car the seal comes within 1" of the bottom part of the door where the fold starts to disappear on the rear door.
 
#47 ·
The upper part of the seal isn't compatible with the adjustment of my doors. I cut the part of the lip of the seal but when closing the door, the front one, both the chromed parts of the upper part of the door are so close that they push this upper part of the seal into the interior, ruining it.

In the end what I did was, cut the whole upper part of the seal and installed it into the opposite door to the one that it was designed to. The seals have like a more thinner part in their endings, and that part works with my doors. So that way it worked, and in the driver door, the one that I did later without having to un-stick it to retry it, it sticked quite firmly. The passenger door after so many tries lost most of the glue. I will try to replace its sticky band with a new one from 3M and if it doesn't fit I guess I will order a new one.

Anyways, this is how it looks in my car. I guess our second-gen doors are rather different. Mine is a Lancia Thema, but it should be by its VIN number just a rebranded 2012 300.

I think it takes off a lot of environmental noise, not just aerodynamically but like if when a car passes besides your car, it's like you hear a lot less of it.

About the length of it, I really believe it's perfect, since as you described, the fold on the edge of the doors disappears at the bottom part of the door, so a longer one would be useless since it couldn't be glued to anywhere.
 

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