Noisy drivetrain - need help identifying
 

I purchased my first golf cart for next to nothing knowing that it needed work. I believe it is a Marathon model. All of the body was missing (replaced with a horrible homemade wood body that I removed and trashed) except for the metal surrounding the area below the seat and metal cover under the dash. There was a manufacturer's tag, Golf Cart Systems, Clearwater FL and serial number 800990 on the passenger's side under dash panel. No EzGo tag other than the motor. EzGo Service Parts Manual X440, X444 no. 2233g-G1 matches my cart with two exceptions. The manual shows manual brake adjusters; mine are self adjusting. The manual shows a split box gearbox, mine is not.

I have refurbished the manual speed control, replaced all electrical cables and wiring, solenoid, and microswitches. New brake shoes and brake cables. Removed and cleaned up brake and throttle linkages. Replaced many rusted nuts and bolts. New shocks. New batteries. Checked gear oil, it was topped up and looked clean. (No drain plug?)

The cart works, just makes some noise. I'm getting a cyclic noise from the rear. Not horrible, but noticeable. The frequency is less than the wheel rotation frequency. It is much less noticeable in reverse. (There is no body on the cart, so the motor, gearbox, and wheels are all exposed.)

Is the noise "normal"? If not, what should I check?

Any help on identifying the gearbox and repair/parts manual for it would be appreciated.