Just wanted to add on to this as I was about to report this bug as well. This was a first person server and it only happens when I zoom in with the weapon. Perhaps it is some piece of clothing causing some clipping issue. I have attached some screenshots to show it in various positions (looking up, then down, then down again), though I did not try to hold Alt to look around.

http://imgur.com/a/sCy40

A friend has this issue too. Found no fix so far.

I had a group of players (but mostly just one guy) who I could hear sporadically for about 5 seconds each time over side chat as well. Confirmed with another player who was next to me that he heard it too.

Just wanted to say that a friend had this issue, his text size in Windows 7 was set to Large. He changed it to 100% default normal, he had to log out of Windows, and when he came back in to Day Z his mouse was showing up and working correctly.