My old Sirius portable receiver sounded like garbage despite the marketing material saying "Crystal Clear". My 2006 Infiniti Sirius receiver didn't sound any better despite being a massive space heater in the trunk. The later cars I've used it in sound good, at least good enough to sound as clear as FM radio or even HD radio. I think some of the channels are still in lower bitrates like the news channels for example, they've always sounded bad. There's something I've read about SiriusXM using terrestrial transmitters which may improve the signal whereas the satellite link may be of lower bandwidth.
