There is a plastic fan on the 930 attached to the motor. You may consider taking off the side rear panel but have caution. The plastic hand wheel is on very tight and interfaces with the drive gear on the main shaft. It interfaces with a screw which attaches to the rear drive gear and secures a washer over the balance wheel engagement spring.
That said, I'm suspecting that the sound is related to the plastic fan wheel on the motor or one of the two belts (notched) are a problem.
Lastly, it may just need to be oiled in the rear area...
Be careful with it, it's very delicate and plastic like...