S-Curve

Figured I'd post here since audio gear is usually pretty susceptible to interference.

I followed the instructions in the tech section for wiring up my Sony/Ericsson HCB-30 bluetooth kit with the built-in audi wiring, mic, and speaker (2000 S4). Made the board for adjusting audio levels and wired it in as well. Everything works great with the xenon headlights off.

When the xenons are flipped on, a rather loud buzzing sound drowns out the mic feed. Nothing is heard on my end, only on the remote end.

I've tried a few things:
-Wiring in-line inductors on the switched and unswitched 12v inputs (single and simultaneously).
-Using wrap-around choke filters for everything coming in/out of the mic circuit.
-Grounding pin 20 (mic shielding according to tech section) to 12v ground.

So far nothing has made a dent in the buzz. The kit works fine when I use the S/E supplied mic and flip on the xenons so it's probably not the carkit or any bluetooth interference.

Anyone have any ideas or insight on how to go about fixing this? Thanks.