Sirius radio & alternator whine

On my first 06 GoldWing I installed a Sirius Starmate Replay radio connected to the Aux input and had good audio. On my second 06 GoldWing I mounted the antenna, audio output, & power connection just the same but I got a noticeable whine from the altenator. I went with the AuxSwitchSet2 from Kennedy http://www.cellset.com/Motorcycleitems.html and it cleaned up the audio just fine. I know it cost more than just a ground loop filter but now I have an easy hookup when I go to add a MP3 player in the future. I guess some bikes have a whine problem & others don't.
Ride Safe
Ken