It's a tradition at Microsoft that when someone leaves for a while, their office is vandalized in one way or another.  Sometimes it is something big like moving the office into the hall or covering it in post-it notes.  Other times, it's something more subtle.  For me, it was subtle.  I returned from a short trip to California and all seemed well in my office.  Then I heard it.  A short high pitched squeal.  Almost as if one of my monitors was not quite in sync.  Seemingly every 15-20 minutes the same noise or something similar but shorter pierced the room.  I tried to localize the sound but it was difficult because it was so short and came unexpectedly.  After 2 days (much of which I wasn't in my office), I had it narrowed down to one corner but hadn't found it yet.  I'd looked inside the computers, underneath the desk, in the legs of the desk.  Still nothing.  I knew it was something my team had done because of their reactions.  When I was in 1:1s with them and the sound happened, they ignored it.  Still, I hadn't been able to figure out quite what it was.  This evening they revealed it to me.  I think I would have found it within another day or so but it was hidden well.  It turns out they had put a small circuit board called an Annoy-a-tron under the leg of my desk.  It puts out a 2 kHz or 12 kHz sound at random intervals.  Well done guys.  My hat is off to you.