From your post I assume you have a Dimension 2350.  Is this correct?  Always post the Model Number and Operating System on any initial problem post.  There are too many different Dell models and it does make a difference for someone to assist you.

Running faster, if it's the CPU cooling fan could be the fan is failing, the heatsink thermal compound is bad and will need replacement or remotely a problem in the BIOS. 

I don't normally suggest updating (flashing) the BIOS but in this case I would suggest this be done as one of the troubleshooting steps.  The Dell BIOS for a 2350 with Windows XP can be downloaded HERE

Assuming this is a Dmension 2350, that model seemed to have problems with the heatsink latches breaking, As a result the CPU overheats and the fans run faster trying to keep it cool. 

Either way, before doing any BIOS updates, power off and unplug the PC. Press/hold the power button on the tower for ~15 sec. Then open the case and check that the heatsink clips are securely latched. Caution: the heatsink will be hot if the system has been running! 

Typically the "hole" in the heatsink base in the 2350  -where the clips latch- gets broken or melted.  I saw the base for this heatsink on the net for ~$10 recently. It can be removed from the motherboard and a new base installed. You can also check with Dell Spare Parts for the base and/or replacement clips, if that's what you need.

Ron

There is no dust inside the system. I have taken a look at the heatsink and the part looks ok. There is no therminal compound between the heatsink and the cpu. There are two metal clips that attach the heatsink to the cpu and the clips look good. They are not broken or bent. The eyes that the clips attach to also look ok. The heatsink is held very tightly to the cpu so there is no ratting around or anything like that. There is air coming out of the back vent although the air is not cold to the touch. What else can I check to eliminate more possibilities?

Do you know which fan is making the noise? CPU fan or power supply fan?

Do yo need some thermal paste between CPU and heat sink?

Failed heatsink? Failed fan temp sensor? Reboot and press F12 before Windows starts to load. Go to Utilities partition. Launch the diagnositcs and run the fan tests.

Ron

Do you know which fan is making the noise? CPU fan or power supply fan? Do yo need some thermal paste between CPU and heat sink? Failed heatsink? Failed fan temp sensor? Reboot and press F12 before Windows starts to load. Go to Utilities partition. Launch the diagnositcs and run the fan tests. Ron

I don't know which fan is making the noise. I do have a graphical type diagnositcs. Is that the one that I should run?

See if you can figure out which fan. Is noise at front or rear? If could be a fan that's dying.

Don't know what you mean by "graphical type diagnostics". Follow the instructions in my previous post to launch Dell's diagnostics which are in a hidden partition on your hard drive.

Ron

Hi,

In your post on 09-13-2009 3:49 PM you mentioned that there is NO THERMAL COMPUND... FYI that there should be thermal compound. Please get some and put it between yor processor and heatsink,

There are many possiblity that may cause your system fan to make loud noise, Assuming you have Dimension 2350.

Check system event log in bios

To check the system event log for errors, perform the following steps:

1. Power up the system.
2. Press the key to enter the BIOS (System Setup).
3. Press the key to select the Advanced tab.
4. Press the key four (4) times to select Event Log Configuration, and then press the key.
   The event log will display any errors that have occured in the recent history of the systems boot processes.
5. Press the key to return to the Advanced tab.
6. Press the key four (4) times to select the Exit tab.
7. Press key twice to exit System Setup and save the changes.

If it does not resolve the issue then replace the fan, if you want that then can try updating the bios and still it does not fix the issue than the issue is caused by the system boards(motherboard).

Note: If bios is not updated properly then it will not allow to use the system and will need to replace the motherboard...

Regards

Dawood

I'll try the suggestions mentioned and report my results. I'm a college student and at this point in time, I have assignments to work on so it'll be a few days before I can report back here.