Firecracker sound that's odd? I had a similar problem with my previous car, like mentioned above, it turned out to be one of the pulley wheels - the one on the tensioner. It only cost me like $7 and was a simple fix - on that car. I replaced my belt on the LS and it was a little difficult because of where the belt is placed. Also, I borrowed one of those belt tools from autozone. Make sure you remove the air filter hose and be sure to make sure the belt is aligned properly. The other thing I found uneasy was getting the belt centered correctly around each pulley wheel. If not, it will zig zag. Definitely inspect each pulley wheel and the tensioner though. Next time, I'll probably just let the dealership do it for all the trouble.