What is the function of the radio PWM lines?

[RBRx]

First off a little back story, I bought a blutooth audio gateway which takes 12v and just outputs audio with the intention of splicing it into auxiliary input on the stock head unit to which I succeeded "sort of". I did this in the middle of the night so I put my parking brake on to not disturb my neighbors with the DRLs and left assuming the surgery was a success... I get ready to take a trip to the store, set my tunes on, then release the parking brake and I get loud pop/buzzes out of the audio.

Image of what was done for those curious... http://puu.sh/oknjr/5c7ad88d3d.jpg

So 2 things come to mind of what may be happening~
A. I'm getting dirty power that gets filtered down the line inside the head unit.
B. Internal RF interference.

These are easy fixes but the problem is how are these two linked to the parking brake (Head unit has no populated wire for parking brake detection)? Also the PWM lines could be related but first I wonder is what is a radio doing accepting PWM signals.... Can anyone shed some light?


EDIT: Nvm I solved the problem yes it was dirty power so instead of soldering onto the 12v+ pin header I soldered it onto the internal 12v rail which has been filtered. After looking at the pinout again I never saw a DIM for the dimmer so that's what the PWM signal was for.