I have a GT5802 and the fan (8015606R) is running on high constantly. It use to be quiet. The motherboard recently failed (took it to Geek Squad) and the motherboard was replaced. I asked them to check the fan. They think it is OK but since their shop is so noisy they can't hear that it is running high. It is loud enough to keep me awake at night (so I turn it off).
Is there any type of head sensor on this fan that perhaps may have failed so that it thinks the CPU is overheating? Are there any other fans on this desktop model?

Usually a fan will run on high when the heat-sink is dirty, or cheap thermal compound is hardened. They can become damaged if they are spun too fast but blasting them with compressed air.

I would remove the heat sink, replace the fan, clean off old compound, apply a thin coat of silver-based compound and put the heat-sink/fan assembly back on (sometimes there is a case fan and shroud).

Good Luck

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