2008 Trailblazer LT. Suspect this was a Fleet vehicle. Bought it used in 2001 from Chevy dealer. Car was in great shape. Everything worked perfectly. About two years ago, I went to play a CD one day and there was no sound. Tried the radio, same thing. Tried the OnStar, same thing. It was as though all of those components and/or all four door speakers had just quit. Then, I realized that the warning chimes weren't working, either. Read on another Trailblazer forum that there was supposedly some module tucked behind the radio (stock factory AM/FM) that mixed all of the sounds from the CD/OnStar & Warning Chimes together and sent them to the radio for distribution to the speakers. Don't know to this day if that is true or not, even after having spend countless hours of researching it. Then, about 6 months ago, I hop in the car, put the key in the ignition (with the driver's door open), and I hear the warning chime. Started the car, turn on the radio and it works fine...same with the CD. Called OnStar for a check...works perfectly. Then I recalled that the forum info I'd read previously said that this "mystery module" was affected by heat and that when it got warm, it'd sometimes work, then when it got cold, it'd go on the fritz. The day the stuff worked was 85 degrees. Did a short tip in the car that day, came home, turned the car off and that was the last time the stuff worked...for about two months. Then, same thing happened. One day, all the things worked again. Next time I started the car, nada. Then one day not long ago, I go to start the car (driver's door open), put the key in the ignition, and accidentslly dropped a pen I had in my left hand out the door onto the ground. Hopped out, bent down to pick up the pen, and what do I hear...albeit VERY FAINTLY...comimng through the driver's door speaker, but the warning chime! Turned on the radio...I hear the broadcast...again VERY FAINTLY. Same with the CD. And, it's the same with the other 3 door speakers. Can hear all the sounds (sans the warning chime...that only comes through the driver's door speaker) very faintly. Note: didn't even try OnStar as I couldn't have heard them and spoken with them at the same time. So now, I have learned that all the components ARE WORKING and that it's merely the VOLUME that's bad. Which, all leads me to more strongly believe that there is some module that mixes CD/OnStar & waning chimes to gether and send them to the radio. Chevy dealership says no, it's the speakers. They claim that all the sounds are "in the stock radio;" that there is no module that mixes the sounds. They say it's the speakers that are bad. I tell no...the speakers work fine...from time to time. Called Chevy parts department and explained the problem. They say there's a VTIM (whtever that is) that sends the Onstar "signals...tones and voices) to the radio and that the warning chimes are "handled" through the Body Control Module. All this said, does anyone REALLY know what the heck is going on here? I swear the speakers are fine. I can hear the radio, the CD, and the the warning chimes, albeit very faintly. Would appreciate any help with this. Thanks in advance!