Inspect the above deck area and deck drive belt path for anything that shouldn't be there such as a branch that may be interfering with the belt travel.
Jack up the machine and look for a bent baffle where a blade tip may be making contact.
Release the deck drive belt and secondary belt tensioners and free spin each blade.
Inspect and spin each idler/tensioner pulley.
Inspect the clutch, its mounting bolt and torque arrester.
With the deck drive belt removed from the clutch and secure so it won't get caught by the pump drive belt, start the engine, turn on the PTO to check for unusual noise.
Spindle lube interval is 40 hours and with a specific type grease.