Sony Vaio VPCY21S1E fan behavior

Hi all,

I'd like to ask you for advice on my Sony Vaio VPCY21S1E that I bought second-hand recently. The CPU fan's behavior is a little frustrating - it switches to high RPM every once in a while. Once the high speed kicks in, the fan reduces its speed to near-zero after a minute or so, only to blast at full speed again in some time (as the temperature increases, I presume) - and so the cycle goes.

I am almost confident the fan should be running with a more or less steady speed, instead of fluctuating that way.

As I said, my idle temperature is ~40*C and goes up to around 45 under moderate stress. The momentary sound the fan makes after speeding up reminds me of automatic fan tests after switching a PC on - it's loud and annoying.

Could a BIOS upgrade help calm the fan down? I don't want it to be absolutely silent - I want it to work smoothly instead of jumping around the speed range like it's doing at present.

Btw. I changed the CPU's thermal paste to Arctic MX-2, but the temperature didn't drop a bit, which is odd. I have another VAIO unit of almost the same model (the 2010 version with Core 2 Duo) and the idle temperature is about 5*C lower there.

Also, some reviews I found on the web say that the temperature in my model shouldn't exceed ~40*C under benchmark stress, with something above 30*C in idle/light stress. So that's less than what I get from my unit.

Any advice will be welcome.