Noise Issues

Has anyone else battled noise issues with an aftermarket system in their 300? I have an annoying tick at low volume levels.

And by the way, it will tick with the engine off (key in Acc position). Heck, it will even tick with the head unit off (as long as the LC8 and AMPs are still powered, of course.)

And I don't think my install is subject to "the usual suspects". Best cables money can buy, good power and ground connections. Cables & crossovers have all been pulled to check for proximity issues. Ground loop isolaters were added -- still ticks. Maybe I should try a flee collar ;-)

I've timed the tick:
tick - tick - tick - tick - tick
Very consistent, 30 ticks every 10 seconds = 3 Hertz.

What on this car runs at 3 Hz??

Thanks in advance for your help with this one. It's driving me nuts.