In case you're like me and can't for the life of you figure out how to turn off the notification sound alert on Mastodon, here is how to do it:

1. Look at notifications tab where you see the notifications from the people you follow
2. Click the settings icon in the upper right hand corner of the notifications that has 3 lines and slider-esque squares on the 3 lines
3. Unselect "play sound" next to each notification type (on my end this changes it from purple to grey on web)

A bit more confusing that other sites but that's how to experience Mastodon without the "doot!" sound upon each notification!