In my 2005 Tacoma I have an aftermarket installation of a Sportster 5 using the direct input adapter and a rooftop "hockey puck" antennae and I'm very happy with the sound quality and reception.
HOWEVER, in my wife's new 2008 Toyota Avalon I have a dealer installed Sirius receiver hooked up to the standard satellite ready cd/radio and it uses the Sirius Interior Glass Mounted Antennae (SIGMA). My problem with this setup is that I get "so-so" quality sound unless I dial down the treble to around 0 or 1 (the range is from -5 to +5). With talk radio (like Fox or CNN) I have to dial it down to -2 or -3. The poor quality is akin to what a torn speaker would sound like - a vibrating or buzzing or rattling kind of noise. The only time I have the problem is with satellite - AM, FM and CD all sound just fine. I'm pretty disappointed with this - the sound is kind of flat. I had the dealer do this installation because my wife did not want anything added to the interior like a Sportster sitting on the dash. The dealer has replaced the tweeters in the windshield pillars trying to get rid of the noise with no success.
Doe anyone have any experience with this problem? Any advice?