New first time riding mower owner here. Just purshased a used riding mower and the second time I used the mower it started to make a strange noise from the drive system after 30 minutes of use, and at first the drive felt intermittent in both forward and reverse and then the drive would not engage at all. It felt like A slipping clutch in a car with a manual transmission. Any suggestions on what I should look at first. Did I burn up the clutch or do I possibly have a transmission problem.