Factory install system in my 2010. Sirius does compress the signals to fit more channels over the same bandwidth. The more popular channels are broadcast at higher bit rates, so it could be that the your favorite channel is more compressed than others. Some of the rock channels I listen you can hear the tinny cymbal crashes. Songs sound like a low bit-rate MP3. For me FM radio sounds better at least for the channels I listen to.

 

Alternator whine can't be attributed to Sirius. And neither can the static. Something else must be going on.

 

That's a ground issue with your truck not your radio.