ok i figure it will be the diff the GT seems to have that prob a whole lot and it has to be tightened every so often...also if you are bashing with this truck i would highly recomend upgrading to the RRP hardend steel diff with the MIP rebuild kit and carbide diff balls as i actually had my diff gear completly melt on me. also a diff rebuild is a rly good idea every 2 gal. or so just to keep it fresh and running like it should