iMac fan

Started my iMac 26" (3-4 years old) this morning and the cooling fan seems to be running at what I would call "high volume and/or speed". The fan noise is quite noticeable.

I've had this happen before but it has never stayed on for as long as it is this morning - so far 30 minutes at least.

Is this normal? Doesn't seem to me that it is.

Any info would be greatly appreciated.

What's running? Look at Activity Monitor and see what's eating up CPU. Flash video also heats up the GPU and CPU so the fans take off. Another big CPU user is Spotlight, which drives the disks hard during the inventory stage.

Did this start as soon as the machine booted up? If so, I'd recommend resetting your PRAM.