New motors may not necessarily come with the capacitors pre-fitted. They are essential.
In case you didn't know, the routine is 3x 0.1uF caps, one from pos to neg, one from pos to the can (usually a little tab on the enbell screw), one from neg to the can.
Caps are widely available from RC shops or if you "think" you are getting a bargain you can probably buy a bag of 100 from an electronics shop.
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