"Chirping" noise on 2002 Mercury Sable

Our 2002 Mercury Sable has developed a “chirping” sound under the hood. Our mechanic suggested changing to synthetic oil, which we did, but the noise still persists. Any ideas as to what is causing the chirping? We checked the belts, and they are okay.

Perhaps a pulley bearing going. Alternator, power steering pump, water pump (if externally mounted) or belt tensioner pulley bearing.

How did you check the belts?
BTW, you might want to seek another mechanic.

Check the cam sensor housing located on the rear of the engine. It looks like a distributor base with a sensor screwed to it. Try pushing sideways on it while the motor is running. If this is the problem it should change pitch.