Still have a goofy HID problem

[Pimptastic]

It sounds like a grounding issue. Do you recall if the flickering they did previously pulsed about as fast as the buzzing you're hearing? I suspect the capacitors didn't fix the initial problem, they merely corrected the light output issue. The relay could still be "buzzing" on and off rapidly because of a bad ground or not enough voltage going to the ballast to maintain the light source. The capacitor is simply storing and releasing power to keep the lights on when the relay opens and closes as it does. I would check grounds and connections.

[300CStick]

It appears as if we (including myself) are all connecting the HID's via the available Halogen connector. Although this works with the 4700uf capacitor, it puts a larger load on the front lamp driver in the front control module. Adding a relay puts even more load on the circuit and perhaps this is why the relay buzzes. I suspect it is not getting enough power to stay fully energized and therefore buzzes. If you have a multimeter read the voltage across the coil of the relay while it's buzzing. If it is not at least 12V there is the problem. I did not install a relay but connected the HID ballast directly to the halogen socket and added the capacitor. This is also part of the reason you need the capacitor. I also installed the HID fogs and they do not need a capacitor. If you examine the attached electrical schematic from the service manual you will see that the FACTORY HID's have a separate circuit with factory relays and fuses connected directly to the battery via a 50A fuse. The halogen control module isn't used except to turn on and off the factory HID relay. I also installed the HID fogs and they do not need a capacitor or relay as they are driven by a factory fuse and relay connected directly to the battery. Again the front control module only switches the fog relay on and off.

This may or may not be your issue but this is how the car is wired with factory HID's.

[LSCto300C]

Thanks for all the help. I'm going to start by switching the ground out and going from there. The odd thing is is that the buzzing has gotten quieter with time but is intermittent in its loudness.
I'm no electrician but I'll be damned if I let this get the best of me.
I'll probably get some HID fogs in the meantime as well.