To summarize the problem is that the heat sink is blocked and since the laptop is running hot, the CPU fan is racing and making noise which will go away once the heatsink is cleaned.
I have pulled out heatsinks to clean that have a 1/8" or more of think lint blocking the airflow in laptops.
The fan races and makes a lot of noise trying to cool but the airflow is minimal when that has happened.
This is a Russian site with the English service manual for the Aspire 5920G, It is probably safe since it is referenced from a site I do use to find manualshttp://www.intellcity.ru/content-2/service-manual-notebook-Acer/service-manual-Acer-Aspire-5920G.pdf
It has a disassembly section and what you would need to do is follow all the precautions in the manual.
If you are feeling brave and are not inept with a screwdriver.
This is a easy one, lucky you.
Before You Begin
Before proceeding with the disassembly procedure, make sure that you do the following:
1. Turn off the power to the system and all peripherals.
2. Unplug the AC adapter and all power and signal cables from the system.
3. Remove the battery pack.
find this section in the disassembly instructions.
Removing the HDD Modules/ODD Module/Memory/Wireless LAN Card/VGA
Board/Thermal Module and the LCD ModuleOnly remove the bottom cover and you should see the FAN
See if you can get the fan out without disturbing anything else. Be careful with the fan power cable. Clean the dust out and put it back together and it should be quiet and cool.
Also don't remove or loosen the heatsink and you should not have to renew the thermal compound and try to avoid removing the video card. The fan usually has only two screws holding it in.
Be careful with Static electricity to avoid damage to the laptop electronics. If you can do the work by a water pipe / faucet or radiator where you can ground yourself before and during that would be advisable.
If you don't feel comfortable doing this Think if you know anyone that does this kind of work.
Edited by rotor123, 31 December 2011 - 09:58 PM.