If you have had your iMac for over a year, you may find this issue. I unboxed my iMac a year and a half ago and set it up on my desk. It's been there since. I usually dust with an extended duster so I don't look back there often, but today I replaced my desk so I broke down everything and moved it across the room so I could set the new desk up. When I got to the iMac I noticed that right where the large hole is for the power plug to go through were stress points on each side from holding the weight of the iMac. There is a very slight bend in the metal where these stretch marks are leaning the mount over towards the monitor under the weight. Clearly with the stress marks dead center of the drilled hole, this seems to have been an engineering oversight as with the metal removed for the hole it is too thin there to support the weight of the new aluminum iMac. You may have this issue if yours has sat for a year or better. I don't think there will be any obvious stress after only a few months so newer owners might not notice this. If I hadn't changed desks I wouldn't have noticed this because really, how often do we look behind these things?