Loud fan noise

My iMac is making a loud 'fan' type noise and seems to be kicking out a lot of cool air from the vent at the top / back of the screen.

I lifted it up slightly to get the serial number from the base of the stand a couple of hours when it was switched off - I'm assuming this has caused some kind of minor upset? I didn't turn it completely upside down. Can I assume that its just kicked a bit of dust around and it will eventually settle down or is this a sign of something more serious?

Many thanks.

The loud noise and the excess cool air is because the fan is rotating faster. Were you by chance running a graphic intensive program or playing a game at the time this occurred?

Download and install the iStatPro widget and keep an eye on the Fan speeds and the CPU temperature.

http://www.apple.com/downloads/dashboard/status/istatpro.html

Regards.