Fan/Noise issue

So the other day I was trying to drain my battery all the way down, running a rediculous amount of programs and the whole deal.

Next morning I plug in my computer and I started getting this small fan noise. Im not really familiar with how the fans are set up in a Macbook, but it sounds like one of the fans is running quietly nonstop. Its not near the sound of them running full power, its just kind of a soft constant sound, and it now happens every time I open my macbook, reguardless of its temperature.

Anyone have any idea what it is or how to fix it?

Just making sure all bases are covered - have you tried restarting the machine?

You may still have processes running in the backgound, even when they don't appear to be.

have you done both recent firmware updates?
(check by going to the apple menu and software updates).

Check you Startup Items under Accounts in Sys Prefs, also check Activity Monitor in your Utilities folder in Applications to know whats running. It'll help you root out your usage.

The macbook fan runs at 1500 rpm at a minimum anyway. Download smcFanControl and run it. It will tell you how fast your fan is running. If it's 1500rpm, then it's fine and nothing to worry about. If it's faster, then the CPU may be busy.