Toro/Exmark 30' stand-on aerator. About 7 or 8 times per day I hear a 'clunking noise' coming from underneath. It seems to be coming from the tines or the hydraulic cylinder area. It's a "metal to metal noise". It started from day one. Some sort of steel is hitting another steel part. It goes away once I back up or something. 28 hours on the unit. Please help.