Drive at a constant speed, then turn on the lights and heater fan full speed. Does the squeal get louder? No change? Belts loosen up after running for a little while due to initial stretch. The serpentine idler belt has one tensioner. You have to loosen the center nut to adjust it, then adjust it with the side bolt to proper tension, then tighten the center nut to lock it in place.


Not responsible for advice not taken...