DIAGNOSIS Debris (like a small piece of packaging foam or dust clump) has been sucked into the main cooling fan or the fan blades are hitting an internal wire. A failing fan bearing is less common but possible.
FIX Power off and unplug the projector immediately. Tilt it gently in different directions—you might hear the debris shift. Use a can of compressed air to blow short bursts into the main air intake vents (usually on the side or rear). Do not insert anything into the vents. Often, this dislodges the obstruction.
IF THAT DIDN'T WORK The noise could be from the color wheel (part of the 3LCD system), but that's rarer and sounds more like a high-pitched whine or buzz. A persistent grinding from the fan area means the fan itself is failing and needs replacement.
HEADS UP Never operate the projector with this noise. Overheating from blocked airflow can permanently damage the LCD panels or lamp. If the compressed air trick doesn't solve it, stop use and contact Epson support.