Are you hearing a thumping or vibration type of noise coming from under the lawn mower chassis? Is it a steady noise or does it get worse when you are driving the mower?
Let’s think about this for a minute. When the riding lawn mower is running, the drive belt is turning. The drive belt increases in RPM when you move the throttle up and down. When the throttle is set to lower RPM, the noise might be louder because the engine noise is less and may be less apparent when the RPM is higher.
What most likely is going on is that you have lost a piece out of the drive belt and when it rolls over a pulley, it creates this thumping sound. If you hear multiple thumping sounds, then you know that there are several pieces missing out of the drive pulley.
There could also be a problem such as a bearing is going out on a drive pulley or the pulley itself could have a flat spot in it or a piece broken out of it. Carefully check all the pulleys and bearings and if they are suspect, replace them.
I hope this helps you find out what is causing the thumping noise in your riding lawn mower and that you resolve it. If you need a lawn mower repair shop, visit our Locations page for help today.