I did the CD AUX-IN hack that l8r did and ectomort showed here:
CD AUX-IN Thread

I was initially very impressed. The sound was great with the silent CD and an Archos MP-3 player. I recently hooked it up to my new XM Commander and it sounds great with the engine off but the alternator whine starts immediatly with the engine. I pulled the power from the cigarette lighter wiring, the constant power from the head unit wiring constant power, and grounded it to the chassis near the shift lever. I tried grounding it different places like the cigarette lighter wiring as well, and had the same results. Once the RCA grounding came in contact with any chassis ground (even not connected to XM) there was whine.
I got a "ground loop isolator" from Radio Shack and that absoulutely killed the whine, but it also attenuated the sound enough that I have to turn head unit to 25 at highway speeds to get moderate volumes.

Anyone have similar experience with this hack and a chassis grounded sound source (i.e. not separate MP3 player)? Maybe it has to do with the soldering or RCA cable I used? I think Crutchfield sells PACs SN-1 ground loop isolator that get a 1.3 dB gain instead of atteuation across it. I might give that a try. Would a filter on the power +12V ACC input wire be better?

Thanks for the help,
Wingnut

Edit:
I took it all apart and removed the RCA ground-loop isolator that was attenuating my signal and instead installed a 4-Amp Automotive Noise Filter Kit (Radio Shack Catalog Number 270-030A) to the constant +12V power to the XM Commander and it killed all the alternator whine and other noise. It is just a choke, I cut my +12V constant power supply line to the XM Commander, soldered the in and the out wires and heat shrinked it up and was done. Problem solved. It also included a 220uF 25V electrolytic capacitor that could optionally be placed between the choke and ground, but it added noise so I did not use it. The part was $3.99. There is consederable room under the center console/ashtray area and I had no trouble cramming all my connections under there. I also added a Y and ran a RCA to 1/8" stereo cable back to the cupholder area for a MP3 player. As long as the MP3 player is off, there is no perceptable attenuation by having both XM and MP3 player hooked into the RCAs I ran to the CD unit.