Exhaust high pitched buzzing sound

[wpendl1]

I just got a 2001 Tahoe LT. I've noticed a high pitched buzzing sound coming from the muffler area, only when the truck is running and it will change with engine rpms. Any one run across this problem? Is is normal??

Also for some reason on the edmonds.com website it shows the LT version standard with the autoride and auto climate control. I'm guessing that can't be right, mine doens't have either of those.

I also read a post about two diffrent size tranny pans. What is the diffrence, and does anyone know why this is so?