I have an 01 A6 2.7 T. Everytime I put on my rear defroster I get horrible radio interference. As soon as I turn off the defroster, the noise ceases. I just noticed it last night so, I have not really got a chance to investigate.

Maybe a bad or loose ground, faulty or sticky relay???

Any ideas or possibleremedies.

 

You're getting feedback from the rear defroster. This deals with a ground issue in the back of the stock head unit. Some one probably had an aftermarket CD player before and when they put it back in the wire are touching each other. Remove the head unit and check the connections.