These fans can be replaced but they need to be adapted because the pin connector to the motherboard is most likley to be a 2 pin connector.
I have just done one this evening for a customer on Gigabyte Motherboard. The fan cost £4.06 and you have to remove the old fan cut the wires and rejoin the cable to the new fan. using the 2 pin molex.
These fans are usually 4cm square. click here have them or even asking at your local PC shop.
Maplin to the rescue. It seems that 2-pin connectors for fans are rare these days, most being 3 or even 4 pin.
After trying to get the connector off to graft onto a new connector-less fan from Maplin (£6.99) I spotted I actually had several 3 pin connectors marked 'fan' on the motherboard so went back and bizzarely they helped me locate the same fan but with a 3 pin connector and mounting screws for £4.99 (go figure!)
My PC is now seemingly silent after i've put up with the racket for about 1 year so thanks to Maplin! (I was too scared to go the oil route!)
Apparenltly it is a northbridge fan BTW.
This thread is now locked and can not be replied to.