John Deer Lawnmower won't start, just buzzes
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