If oiling the motor doesn't help, and if you haven't done so yet, I'd suggest removing the 3 bolts that secure the fan cover plate to the fan housing and pull the whole assembly out. You then should be able to do a quick diagnosis, or at least rule out things like fouled or bent fan blades, loose fan connection to shaft, inadequate fan clearance, etc. There's no harm in having a spare motor, but it's also good to make sure you know what you're dealing with. There's also no harm in checking the transmission oil level, and making sure it's synthetic or reasonably fresh regular oil. I was surprised by how much an oil change affected the racket from my (still-noisy) 85R.