Mostly when 2001 LT Tahoe 5.3 is in a low speeds like parking lot speeds, in reverse, and pulling off, sometime even just my foot on the brakes, I have a resonating sound that seems to travel from front to rear. I suspect it is exhaust/muffler related, (I am still on the original muffler but no emission test issues) and I've tried to strap down the y-pipe, but it still has this noise. The noise doesn't occur when I'm higher than 15-18mph. Some have suggested that its heat shields and that I should remove them but I dont have any idea on how or where to access them. I went to a shop and the guy there says that he and his bnl have the same issue and haven't been able to locate the source of the noise. I was once told that the muffler has internal fins that can come loose and that compressing the muffler a just little bit could help. Any ideas?