Any idea what could be causing this? As soon as I turn on the button, only when the radio is on, I get static, the station cuts out entirely. It's a Symphony Radio in an 01 a4. Thanks!

Tim

 

Tim, maybe someone with an A4 will answer. My A3 has the antenna in the rear glass along with the defogger wires. You may want to start with the antenna amp and the defogger wiring sharing the same area if that's the way your car is. From your description it doesn't do it with another source like a CD, so you may need to concentrate on the antenna feed.
Does your rear window defogger work? If not that would be were I would start. Good luck with it.

 

Is your rear glass tinted? The solution some tint places use doesn't dry up completely and since your defogger and FM/AM/Key remote antenna are all along the back glass the amperage along the defogger causes interference with the wires in the FM/AM antenna section. Just something I have seen before. The only other option is on the left top side of the glass under the rear roof trim piece is your antenna selector(diversity) box which could be malfunctioning because it must contact the glass wires to properly pick up the radio antenna wires.