Excessive Fan Activity - High Performance Mode

I have a macbook pro 15" 2009 model

It works brilliantly, no complaints I love it.. in battery saving mode!

When its in high performance mode the fan goes nuts!?

I've checked activity monitor etc and nothing is using all the power, theres no reason why the fan should be working harder than it does in battery saving mode.

I always have open.. Adobe Fireworks, Chrome and Finder.. Thats pretty much it. And in battery saving mode everything works great, the fan is quiet. Why when I select high performance for a bit extra speed maybe does the fan speed increase tenfold? Dosnt make sense!

Anybody come across this?

Thanks