Noisy could be either a failed fan bearing, or fan that is grinding against something like wires inside that are mismanaged or a heatsink clogged with dust bunnies.
In one system a while back the customer told me that it was making a grinding noise like someone turned on an electric grinder inside of it and then it would shut down after like 10 seconds. When i opened it up I found that the 4 locks for the socket 775 heatsink were snapped off the motherboard and the CPU fan and heatsink were resting fan blade down in the case so when it was turned on the plastic blades were grinding the bottom metal and the heatsink was dancing hanging from its power connection on the motherboard.
Perform a visual inspection inside to make sure all looks good, nothing in the path or conflicting of fan blades and heatsinks attached properly vs resting face down on bottom of computer case.
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