I have a mid-2011 MacBook Air and recently, its fan has been going absolutely crazy. When I use it at a table for around 45 minutes, the fan sounds like a Roomba stuck on a wire. The sound gets progressively louder, and I really don't want to see how it progresses after that. If I wait for around 30 minutes to an hour and then use my computer again, the fan doesn't make the "Roomba + wire" sound until about 45 minutes later. This issue has been going on for two days.