4wd vehicles may develop a squealing noise coming from the front wheels when driving below 30 mph. This is generally caused by dry excluder seals, lubricating the seals will commonly correct this concern.Google+
Car Problem Reports
Ford Explorer Dry Excluder Seals May Cause Squealing in Front Wheels Under 30 MPH
Ford Explorer Problem
Average Mileage: 76,675 mi (10,000 mi - 200,000 mi)
Visitor, 2001 Ford Explorer
Squealing noise is noticed intermittently from front passenger side wheel area only at low speed, especially when it's cold. Nothing wrong with the brakes or wheel, or any other reason for the noise.
Visitor, 1999 Ford Explorer, 10,000 mi
Dealer removed wheel bearing and applied grease to axle shaft bearing seal.