Can you tell us if you know which fan is loud, Is it one of the case fans or the processor fan?
Also when you hear it is it a sound like it is spinning hard or more of a whirring/grinding sound?
Let us know
There are a couple of things that might cause this type of issue,The first is that the machine needs a thourough cleaning, If this is the case then using a can of air to cleanout the inside of the case with the machine shut off paying special attention to the main processor and heatsink shoul dsolve the issue.
If you try this and the processor fn still spins heavily then it is probable that the thermal grease between the processor and the fan heatsink, If this is the case you will need to shut down the machine and then carefully remove the fan and heatsink from the processor.
Once the fan is removed carefuly clean off the old thermal grease using a soft paper towel after you have grounded yourself against a metal object such as a faucet.
Next you will need t apply a pea sized amount of fresh thermal grease (available from radio shack) and reseat the heatsink
Once you have done that let us know if the fan is still overspinning.
this did not fix the fan
Can you tell me if you changed out the thermal grease on the heatsink?
Also does it do it constantly or after some time?
yes I have changed out the thermal grease it doese it all the time
In that case it sounds like the Dell Hypercool in the BIOS is causing an issue with the fan and makng it run full on all the time, We can try installing a newer BIOS from here and seeing if that stops the issue, If not we may need to look at replacing the fan and heatsink with a quieter and lot more efficient unit such as a Thermaltake http://support.dell.com/support/downloads/driverslist.aspx?c=us&l=en&s=gen&ServiceTag=&SystemID=PLX_GX280&os=WW1&osl=en&catid=&impid=
Try updating the BIOS and let me know what happens.