I have a JD L120 with 200 plus hours on it. I get this vibrating noise from under the seat where the transmission is when the break pedal is not pressed. When I press the break pedal slighty, just barely engaging the break, the vibrating noise disappears. It's loud - almost as loud as the engine when it's on it's lowest throttle setting. So far, performance has not been affected. Any ideas if this can be fixed, or is this just old age?