Diagnosis
The projector's internal temperature sensor thinks it's overheating, forcing the fan to max speed. This is usually caused by a clogged air filter.
How to Fix It
Power off and unplug the projector. Locate the air filter on the side, remove it, and clean it thoroughly with compressed air or by gently vacuuming. Reinstall it securely.
If That Didn't Work
The internal dust may have migrated past the filter, coating the heatsinks. This requires disassembly for cleaning, which is a professional service job.
Heads Up
Never run the projector without the filter installed—you'll guarantee a dust-clogged lamp and optics, leading to a much more expensive fix.