The pulley feels tight, so I am guessing it is not the coupler as I originally thought. I do notice that the pulley spins while the engine is running, I guess just the air flowing from the intake turning the guts of the blower. It is fairly strong if I snap the throttle. Is this not enough to cause the bearings to make noise? I can try taking off the other belt and see if the noise goes away. It does seem to be quieter, but did not go away with taking the SC belt off.