Dimension 9200 (CXP061/XPS410?) main fan at full blast, but temperatures are OK. Sensor issue?

Hi,

My main fan (the big one at the front) is blowing in hurricane mode, despite the fact that the system temperatures are OK. It starts blowing hard right from cold boot after the computer has been off for nearly a day (i.e. it can't be overheating).

Additional info:

- It is not sitting next to any heat source.

- Airways are clear.

- This happened for a couple of days before Christmas, then cleared up and came back again yesterday, all without me opening the case.

- Bios is up to date (2.5.3).

- Running Vista 32 bit.

- SIW (System Information for Windows) gives me the following as temperature readings: CPU0 24°, CPU1 28°, GeForce 7900GS 48°, HDD1 29°, HDD2 40°.

- The system is not overclocked - all is as delivered.

- The bootlog has recorded an error at boot ups coinciding with this problem: Air Temp Out of Range.

It cannot be so hot straight after a cold start, so I assume that there is some kind of sensor-related issue.

Any help appreciated! Thank you.