hey friend.

If all your gears look fine I hope you didn't drive through water.. or get it wet. This can cause the speed control to send information to the motor erratically causing it to vibrate making just noise.. or check the pinion gear grub screw.

Check all the gears in the differential I'm sure your perfect here..but make sure they're not too far apart because under the power of this car they may feel good but might skip.. you should see signs of skipping but sometimes it is a little tricky for a beginner.. because it won't be broken or anything. Make sure that the cases are tight and gears are tight.. if you do find this problem make some shims out of something. Or buy something to use.

It also could be your dog bone cups somewhere else slipping.


Just trying to help... can't really think of anything else.