laptop's making a mental noise

[Barely Human]

If its not coming out of the speakers, then realistically you have to put it down to the moving parts.

This could be either:

Hard Drive
CD Drive
Floppy Drive
CPU Cooling Fan
Any other system fans

Failing hard drives tend to have a very distinct sound to them, so see if you can record it like C.O.Prodigy said.

[C.O.Prodigy]

Failing hard drives tend to have a very distinct sound to them

That's what I had in mind... +1