I have a 2007 LT, my speakers have been going in and out for a year now, and so has the light in my gear shift indicator. The first time this happened, Chevy installed a new speaker and it worked fine for a while. Then it happened again to another speaker. I'm pretty sure it's loose wiring. I know for sure I have a loose wire somewhere near my heater fan, I can hear the fan hitting the wire. It is very annoying. Every now and then when I turn a corner things start to work properly. I have dealt with it for a while because I wanted a speaker upgrade anyways (which is coming next week).