it sounds like it is not sounding so good. perhaps the handpiece
is pushing the inner spinning cable inside the flexible sheath.
causing the armature to be out of alignment, causing all this
remove the handpiece from the sheath and try running your flex
shaft. if the noise stops, you can adjust the sheath yourself by
loosening the set screw located directly below the motor where the
sheath connects to the motor housing. with the motor running at a
medium speed and the handpiece connected, move the sheath downwards
until the noise stops and retighten the set screw.
if the noise didn’t stop, be sure nothing is displacing the
armature. if it can’t be figured out, call the supplier.