I removed the old fan from my dead HP a6000n and installed it on the new ASUS CM5570 which only has 1 fan/heatsink attached to the MB. When I installed the old fan which used to be quiet on the HP to the new ASUS, it runs loud nonstop afterI turn the PC on.

Do anyone know why is this happening? The fan was really quiet when I used my old HP.

Old PC Spec: Vista Home Premium 32-bit, 3GB ram, Radeon HD 2600XT 256MB, 300W PS, Dual Core 2.2Ghz 1M L2 Cache,
New PC Spec: Vista Home Premium 64-bit, 6GB ram, Onboard Graphic Intel GMA X4500, 300W PS, Dual Core 2.6Ghz 2M

Does it have anything to do with the specs? Fair comp knowledge here.. so help please

Is it the cpu fan or northbridge?
Either way it is controlled with the bios unless it is connected to the wrong header on the mobo.
In the pc health section of the bios there should be settings to allow the adjustment of the cpu and nb fans as per what the relevant temps for them are. If the fan is connected to the correct header, the fan is probably set to run flat out at a lower temp than the old pc.

Sorry forgot to mention, its a case fan on the rear panel

The case fan is connected to a 12 volt connector, so will run flat out all the time. You can slow it down by moving the red wire in the fan connector to the 5 volt circuit of the 12 volt connector.

dirty fans is equal to noisy system.. :) <snip></snip]