I just fixed this very same noise issue. All you need is a Philips screwdriver. Open the case. suck out any dust in the case. Particularly suck the dust on the processor fan and wipe it clean with a cloth. use the screwdriver to reseat the fan. What I did was to unscrew the four screws holding the fan and then screw it back in tightly. I think they loosen up after a while. The cooling mechanism needs to be tight against the chip.
This significantly quieted down my computer. Sorry for this delayed response. Also, would like to know how to upgrade the processor. I have a I7-920 processor.