Just saw Johns reply and wanted to clarify. It would literally be impossible to clamp the spinning turbines too tight causing a grinding noise the way the motor
is supposed to be mounted within the base of the CUB. The original mounting process requires a foam cushion at cool air intake, and a T-Clip to secure the motor housing and not around the turbines which would cause excessive compression on the blades. In addition, a ss secure bolt is used to help stop any compression against the inter base where turbine enclose meets.
Having done hundreds and hundreds of those mounts causing no compressions of any kind, I would suspect that either the Foam cushion, the T-Clip, and /or the ss secure bolt was not installed, or
re-installed improperly, period.
Thus causing this unbearable noise. No other way really.