Motor runs fine on a stand - doesn't move on the ground

[Radcliff]

Gentlemen, I was hoping to pool some of the vast knowledge out there. I just put a new brushless system in my car and it goes like a champ when on a stand, but put it on the ground and all I hear is a high pitch chirp...and the motor spinning.

Any ideas what is going on here?

Thank you all.

[necronomicon]

If the motor is spinning, could it be  a loose pinion gear?, are the gears meshed properly?-

just a thought

Neil