Put quite simply, my system is as loud as a blow dryer at idle and noticeably louder when under load. Speed Fan reports that the stock AMD CPU Fan is running at 5200 RPM at idle and 6300 RPM at load, there's also some fairly obvious vibrations that can be felt if you put your hand on the chassis.
Other Specs & Information
CPU: AMD Phenom II X4 955 Black Edition @ 3.2 Ghz
CPU Cooler: Stock
MB: Asus M4A785-M
Chassis: Antec Three Hundred with 1x 140mm, 3x120mm Antec Tri Cool Fans
I've had this computer in the same situation for over a year now without this problem, last week I swapped my GTS 250 for an Asus 6850, did my annual dust cleaning and only encountered this problem today. From searching through the forums, I'm inclined to believe that I'm one of the many who complain about the very loud AMD stock cooler, what I don't understand is why I am only seeing this problem now.
Temperatures don't seem to be overly high as it idles at around 42C and reaches 63C during a Prime95 Torture Test.
I plan on re seating the CPU Cooler & re applying Thermal Paste tomorrow, but that doesn't work out does anyone have suggestions on a replacement CPU cooler, preferably under C$30 (Canadian Dollars) as my budget is quite limited at present. I have no plans on OC'ing, just want to bring the noise level down
A 92mm fan should solve your noise problems under budget, a couple dollars more will buy a 120mm cooler like the Xigmatek Gaia which is very quiet.
Why now? As DM suggests, perhaps the fan [bearings] have simply worn out. If your temps are not any higher, I'm not sure what else it could be. If your temps ARE higher now, the old TIM could have dried out, but I still think a replacement would be your best option (if you can afford it).