I have the 2005 LT model and love the ride but I have a very loud humming/roar sound coming from the back of the car. This took place 1 year ago and I replaced the tires and the sound subsided to next to nothing. Now its getting loud again. From my simple observation the tires look even with no unusual wear, No vibration noted, The sound increases as speed increases, The noise appears to be a little more on the right rear, I have only replaced the tires and no other modifications done to the car and it has 110,000 miles on it.

 

Sounds like the tires to me. I've been thru that issue myself. Are you rotating your tires every 6,000 miles? What tires are you running?