Hi,
Without detailed information about your test and measurement steup we can only guess.
RPM, anti aliasing filter, measurement time, sampling rate, windowing function, complete results...
It could be a measurement error, like alias frequencies,
It could be the the balls of the bearing.
But a correct setup will show you a lot of good informations.
There will be noise, but there will be a lot of true overtones.
Btw: FFT on the motor current is done with reliability pumps for example, they early detect bad bearings, defective propeller and so on.
Klaus