Lack of air flow in room causing PJ fan noise?

Hi, I've got an Optoma HD73 and it's driving me mad . The problem is that when it is ceiling mounted or held anywhere near the ceiling the fan whirs up and down. Optoma tell me it's an environmental problem - there's no air flow in my room. They may have a point - my 14' x 8' home cinema room is all double glazed and when I watch movies I do it with windows and door closed. Today is not a hot day and with the door open the pj was nice and silent, but when I closed the door to my room the PJ started whirring up and down again. I don't know whether another PJ such the Mitsubishi HC3100 would be as temperamental - I know that my previous HD72 wasn't. So my last resort before flogging it will be to mount a small (hopefully silent) fan a few inches from the PJ blowing air around it. Do you think this will work and are there any other options? This is apparently an environment rather than a PJ problem as Optoma say there's nothing wrong with the PJ.