I freaking love Mastodon, but I hate the annoying beeps that constantly play when viewing Mastodon on a web browser. If you’d like to turn off all those sounds, you can click on the “Notifications” button on the right side, then click on the little settings icon near the top of the screen. From here, you can scroll down and disable all the “Play sound” options. I think you need to click the checkmark near the top of the screen. If you are still hearing the sounds, it’s probably because Mastodon is still open in another tab. If so, quit the browser, and then it should be fixed next time you are on Mastodon.