Depending on the board you have, you may be able to set the fan speed by software that comes with the motherboard. Since this started after you moved it about and blew "out" the dust, it may be that what you blew ended up inside the fan sleeve, causing the RPM's to drop due to increased friction. The software may require the fan to rotate at a given RPM when the CPU is at a certain temperature. I think the easiest thing to do is to just swap out the fan and see what happens. They are not expensive. If you can't change the fan without also changing the CPU heatsink, you might want to remove them both (don't forget to ground your hands to the case first) and then clean them with compressed air. It may be if you have a sleeve fan instead of a ball bearing fan, you cannot lubricate it. The fact that the CPU temp has not changed much leads me to believe this is simply dust in the fan. If you can, get one with ball bearings instead of a nylon sleeve. They will last longer as a rule.
In 2001 when I bought a PC with a 1ghz AMD CPU, I loaded the motherboard CPU temp, and fan speed software, (From Asus) and ended up taking the PC back to the vendor 3 times before they put on a heatsink and fan large enough to prevent the CPU from exceeding the recommended temperature. The fan and heatsink I ended up with were more than twice as expensive as the one they supplied me with originally. That could explain why they preferred not to load the control software with the systems they were selling.
Sincerely,
Mr Paul
