Ok so I have been enjoying the Mac Pro for a few weeks now and just recently I started to hear the annoying buzz sound at the back of my Nehalem Mac Pro. At first I thought it was the power cord. Whenever I pushed it in a bit harder the buzzing noise would stop (some of the time). Then that was ruled out. The second deduction came down to the buzzing noise coming from the internal harddrives. But whenever I open the case its virtually silent again. Then I found the culprit just a 30 seconds ago before posting this! Its the latch!! Whenever I hold down the latch or touch it with my finger the buzzing noise stops immediately. The latch seems to not go in all the way and has a small (1 mm) from snapping in completely. Well it looks like its snapped in all the way but if I press my finger against the latch it will move in about 1 mm more. Anyway I just keep the latch unlatched (while the side panel door is closed) and the noise is gone forever!! Update: whoa I didnt know that if you unlatch the latch and then below it flip down the lock mechanism down, you can closed the latch and put a lock on it! Anyways now the sound is completely gone. I think the latch was laying on top of that mechanism that flips downwards and was causing the vibration against it.