Nasty sound during xon startup

Demo vid https://www.youtube.com/watch?v=TxoYBKPP6Rs&feature=youtu.be

It's reported by different people for different versions.

On OS X this sound is heard during (almost) every single launch no matter what the Xonotic version is (release, autobuild, git).

On Linux some people reported to experience it occasionally, but after the commit 3bd7661c it appears regularly (as seen in the video mentioned above).

Nobody reported this issue for windows yet.