Hello, noises are impossible to guess at online! Hands and ears on inspection is needed to sort out what is going on. You could have any pulley making noise, a drive belt making the noise. Your Mountaineer does not have a "timing belt" so that is definitely not a possibility.
RepairPal Certified shops can diagnose and repair your 2005 Mercury Mountaineer. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
