The factory 6-disc changer in my A4 didn't work when I bought it, so I replaced it with a JVC deck. I installed it myself, with the help of a more mechanically inclined friend. Ever since putting it in though, I've gotten a weird humming/buzzing noise through the stereo. It seems to rise and fall with my engine RPMs. Any idea what might be causing it?

RFI - radio frequency interference is my guess. Dont feel like elaborating

check the ground

Ground was my first thought too, but I have no idea where the ground connects to. Do you know?

Im new to Audi's but the sound is definately from a bad ground. Follow the ground wire from the Radio to see where it goes. If it goes to the harness/somewhere you cant see, run a second ground to anything metal behind the radio.

Just ground itit's he metal bar behind the dash. it's a black wire out of the back of the head unit