Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Not sure what the humming noise could be as the only things operated when turning key is power to solenoid and then to starter. Only part that I would think could make a humming noise would be the starter if it was not engagingthe flywheel and just spinning. You have got me baffled as well, as I have never heard a mower produce a humming sound when start was attempted.