Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
Have you ruled out the two drive belts and the variable pulley that goes between the drive belts? Nothing rubbing on the drive pulleys? If it is not the belts or pulleys, you may find noise by raising tractor on the jack stands and run unit to see if you can determine side.
I see question is still open, did you find the noise?