Rear diff probably too tight, a Car tweaked.... The ntc3 has that tweak problem, but I sort of solved it by running 40shore foam Tires on the left side, anc 37shore foams on the right side...... Make sure your front diff is tight, and your Tires are shimmed properly. Also reduce your steering rack play, and make sure nothing from the steering system is rubbing the rotating shaft parts..... The ntc3 spool is better than the diff up front, specially when you can put losi lcd's (#3344) to stop chatter, without any Mods at all... The spool will make your Car accelerate straighter and faster too....