After a couple hours of riding my longboard it started making a high pitched squeak\squeal which sounded like it was coming from the brushless motor. After some investigation I found that a circlip on the end of my Turnigy Aerodrive SK3-6364-245kv Brushless motor was making the noise. The circlip usually rotates with the shaft of the motor but the motor bracket was stopping this from happening.

Close up photo of circlip on the end of SK3 motor

I used the DIYElectricSkateboard.com website “support chat” and spoke with Dexter the very helpful owner of DIY Electric Skateboards and he suggested trying washers on the 4 x bolts which attach the motor to the bracket.

Longboard Motor with Spacers

I used 4 x M4 washers and the circlip now rotates freely which appears to have fixed the problem.