Just bought our first '02 Ford Explorer XLT, 53,000 miles. Drove it off the used dealers lot and after about 1/2 hour a loud squeal started coming from under the hood. If the vehicle idles, there is no squeal. If you raise the rpm's while stationary, or while driving, the squeal gets worse. If you turn the A/C on, the squeal is not as bad as when the A/C is off. Will take it back to the dealer but would like to know if anyone else has had this problem and what should be done to fix it. Tried some STP belt conditioner, didn't seem to help. Oh...4.0 Auto Trans, 6 cyl., 2 wheel drive. Thanks all!

 

Your belts might not be tight enough or they are glazed and need to be changed

 

Probably a belt tensioner. Serpentine belts do not like anything sprayed on them, just makes them worse. You might look at the belt to see if it has cracks in it and replace it at the same time.