jaspirr

I've done some more research and my opinion is somewhat similar to yours. I'm pretty positive I have a premium sound system, I'm fairly sure there is a factory amp, and I'm fairly sure that has something to do with my whining sounds. I know next to nothing about audio so forgive me if I'm sounding like an idiot. From what I've gathered on google searches, I could have an issue with the RCA plugs that go into the back of the headunit. I think those have something to do with the factory amp. There is some grounding issue with them, or some interference issue where the RCA's are too close

It does work without the ground wire well...grounded. I always thought that was odd but didn't know what it means. I did the install a few months ago so I'm having some difficulty remembering exactly how it was all wired. I bought a Metra 40-VW54 Amplied Antenna Adapter and attached that to the headunit as per instructions from an Audi website. I'm not sure if that has any effect on what you're mentioning.

anyone have any ideas?

nope, just the headunit with everything else stock. I also have the GPS antenna sitting on a metal platform near the fuse box. Don't think that could be the cause of any issue but figured I would mention it.

I installed the AVIC X920BT in my 2004 Audi S4. When it's hooked up, it causes this high-pitched whining/whistling noise that goes up and down according to the engine's RPMs. It is very noticeable at idle and at some points it becomes even louder than the music I'm listening to. It sounds like a combination of radio interference and a supercharger. I've been told a bad ground can cause this. I inspected the headunit's ground today and sanded down the whole area around the bolt to bare metal, but the sound still persists. Someone on another forum recommended that I might need some type