VERY interesting!

"The cable that came with my kit (ie from BMW) has the common ground (the tan and white wire) assigned to pin 2 - which is a null pin for the receiver. The common ground is pin 3."

I was checking voltage and grounds and I kept seeing a negative resistance on that pin instead of normal resistance. I'll have to check that out. I'm sure this won't fix my overall Sirius problem, but if it gets rid of the whine, I won't have to disconnect it until I get a new CD unit.