We've got an oldish riding lawnmower we bought along with our new house from previous owners. It started up and worked a couple of times but now won't start. It just buzzes. None of the videos I can find online reproduce this sound so not sure what might be wrong.
Here's a video of it not starting https://youtu.be/-KvItIj6Hlo
Best Answer
Its your starter, more precisely, the starter mechanism (clutch/bearing) is not engaging the engine. It can be misaligned, broken teeth, foreign debris stuck in the mechanism, or just dirty and needs cleaning/grease.
Here's a quick youtube so you can hear it per request: https://www.youtube.com/watch?v=1trcMQFvvWU
There are a ton of videos on this topic out there, but once you inspect the bearing it should give you an idea of the issue.
Here's some more detail on it: https://www.youtube.com/watch?v=RhdSq4WOaDM