To quiet a window air conditioner, it is necessary to first diagnose what is causing the noise. One possibility is a malfunctioning fan. Open the unit, and locate the fan. Clean the blades, and correct any loose ones by tightening the screws at the base. Check to make sure the blades are not bent, and gently straighten any that are crooked.
If the unit is making a humming or grinding noise, it may need lubrication. Unsealed motors can be oiled by applying SAE 10 in the oil ports. This type of lubrication can be done annually or seasonally to extend the life of the unit.
Another possible cause of the noise is loose screws. The vibration of the air conditioner can loosen screws in the mounting or internal panels. This is easily corrected with a screwdriver.
If the unit has collected dirt or debris, the coils may be dirty. They can be cleaned with a vacuum cleaner or a soft brush.
If the coil fins are bent, use a fin comb to repair the problem. Insert the teeth of the fin comb between the coils to straighten them.
Noisy air conditioners can usually be fixed by the homeowner. If the problem persists, call an HVAC repair service.