When in a lobby, and usually if you have the chat up, in any section, getting cut from the host or leaving yourself, you will start getting a really annoying and random beeping sound, the sound of one of the menu sounds.
this is caused by having the scroll bar go to the bottom of the list of who is online, and each time someone leaves/enters it will move the bar a bit, causing the beeping sound.
this has happened to me for months now and it has made me close the game and reopen it with rage.
to fix it: Go into chat and find the right hand section where it shows the users, and click and hold the scroll bar and scroll it up to the very top. this will stop the incessant beeping. :)