Wiring in a rx, an ESC and a battery (pack)
(Sorry - more questions!!)
Do you get the same noise in both forward and reverse?
Try a drop of light machine oil on the motor bearings.
Which motor is it?
Then move back along the shaft input and output.
Is there any slack in the coupling joint?
If so a spot of grease helps quieten it at least, if nowt else Vaseline will do.
Cheers Doug 😎