I have my Sirius set up like Morphius above. I have used a cassette adapter and now a GTA car kit type direct into the CD harness input . Using either the 3.5 mm jack or the iPhone power input and before that the cassette adapter I get an annoying whirring which seem to vary in intensity to my engine rpms. I remember a similar issue with my 1970's era Pontiac ( my first car) with an aftermarket cassette deck (pretty cool in 1979). Does anyone have any ideas how to get rid of this sound or is it something that I have to live with. I am willing to go to a new head unit. Does anyone have a good suggestion that is a plug in replacement that has Sirius or XM module built in or does that have to be purchased separately like it was on the Clarion unit on my boat. Thanks. I may have to start a new thread to get responses but I wanted to get responses from the previous posters on this thread if I could.
I actually found my own answer, alternator noise, and I will check if my power wire and input wire are running parallel and make sure they don't.