http://www.AutoWerksofAmerica.com/ Replacing a BMW tensioner is easy. This video uses an E36 M3 as an example of how to replace BMW tensioners for both the driver’s side and passenger side. The tensioner wheels and the idler wheel also get replaced.
Remove the plastic bits from the underside, the cruise control mechanism, air box and fan to get access to both belts. Remove the passenger side belt, then the driver’s side. Check for cracks and prepare to replace them as needed.
If the pulley wheels spin freely, they’re going bad and should be replaced. Chasing down the true source of your under-the-hood squeal can be a painful trial-and-error experience.
After the tensioners have been replaced BE SURE that the belts are correctly installed and aligned.