i had a similar probl;em with my LST - turned out it was the diff cases had cracked and the teeth were hitting the case, as it was being warped everytime throttle came on....

hope that made sense - ummm - look at the diff case for cracks etc -lol-

btw, if it's any help - it was a VERY small hairline crack in my diff case - making it pretty tricky to find :)