A31 : fan is running : should I worry?

[emeu1]

Hello,

the fan on my A31 almost never ran, well maybe it did but almost never audible.
The only times I sometimes heard the fan running was when I used GIMP.
But never when surfiing the internet (I use Mozilla), doing word processing or sorting the pictures I made with my digital camera.

Now, since a week of 2/3 the fan is constantly running, even when the A31 is only turned on.
I haven't made any hardware changes, nor did I install downloads from Lenovo.
Task manager shows a CPU load of 0 to 1, occasionally 2%.
The A31 doesn't get hotter then before.

I've scanned the laptop for malware (Spybot, latest version) and virusses (TrendMicro OfficeScan, latest version).
Nothing found, laptop clean. I use Win XP Pro, SP3.

Should I worry? Is a hardware defect to come?
Or has anyone a clue why the fan is now constantly running and how to fix it?