I suspect one of the spindles is seized a bit and/or Belt is too loose. Get it up in the air and with Blade rotation OFF, reach under and see if they rotate with equal ease. Sorry for your luck. Check what was done on last service call and get your BF to man up.
It isn't a Reactor. A couple swipes on the bench grinder Coarse side and done. No need for razor sharpness which will dull quickly. Balance if you can.
Engage the Parking Brake and flip seat back. + to +. Do NOT jump with a vehicle with the vehicles engine Running. Catastrophic failure of your Mower Stator can result.