I've noticed that the fans on Northbridges as well as the fans on video cards seem to have this problem quite frequently. I believe it to be a combination of size (smaller fans have relatively tighter tolerances), quality (anyone seen a stock fan with ball bearings?) and dust. Yes, dust. No matter how dust-free you think your house is, your system WILL collect dust.
I find this insistence on using active cooling to be ludicrous. Many of these devices do not need active cooling. What's even worse is that a device designed for passive cooling will get a smaller heatsing when outfitted with a fan. If the fan were to die, the heatsink would thus be too small to cool all by itself. I've seen video cards get burnt out because the fans died. Did these video cards need fans? No. I had a Geforce2 MX that had a decent heatsink and NO FAN, and I overclocked the snot out of it and it never had a problem.
I wish motherboard and video card manufacturers would use decent heatsinks and skip the fan
in instances where the chipset manufacturer doesn't say it's needed. As I recall, I saw some Shuttle i845 chipset motherboards (forgot which model, it used SDRAM and not DDR) that had these nice tall heatsinks on the Northbridge without fans. This would be ideal If I can find a source of heatsinks like this besides at
this overseas place, I'd probably score me some.