Just to get everyone caught up I just got off the phone with the owners son at the tractor company who said all yanmar PTO sound that way and he cant explain why but it does. He also took a video for me to show me that even the ones on the lot sound the same way.
I just bought a 2022 sa324 and having the same issue. It sounds like 2 gears that are not synchronized if that makes sense. Did you ever get yours figured out