With a unit that old I would bet the heat sink (i.e, the radiator) is clogged with dust and so no longer dissipating heat efficiently. Dust build up in the fins of the radiator cause the fan to run more often, harder and louder. The solution to that would be to blow compressed air back through the radiator in the opposite direction from which the air normally flows. It would have to be done carefully in short bursts of compressed air with pauses in order to keep from overheating the fan bearings. Sustained blasts of compressed air will spin the fan too fast and too long and will fry the lubricant coating the fan bearings. Ideally, this should be done with the laptop partially dismantled so as to expose the fan. This would allow the dust to be more completely evacuated from the interior of the laptop but I have often practiced this procedure with success without a partial dismantle. There is some chance that not dismantling the laptop to blow the dust out may cause dust bunnies to lodge in the fan blades and prevent them from turning.
So the first step in the process I have outlined is to locate the exhaust vent in the laptop case along the edge of the bottom half of the clam shell. If you shine a flashlight into it you will see the radiator fins. The direction of the compressed air bursts would be from the outside into the interior.
