knocking noise from serpentine belt area

Hi this is Dusty, I'm one of the auto experts on RepairPal's Car Genius team! Hey! Dealing with a knocking noise can really throw a wrench in your day, huh? You've already done some detective work by narrowing it down to the serpentine belt area—smart move! Since the noise vanishes when the belt's off, it's likely something directly related to the accessory drive system. You've already swapped out pulleys and belts, but the issue may be originating from one of the other accessories tied to the belt. Be sure to check the alternator, water pump, etc., typically you'll be able to rock them back and forth with your hands if they've begun to fail. You can use a mechanic's stethoscope (or a long screwdriver) and spin the pullies manually as a secondary means of confirmation. It's worth double-checking the alignment of everything as well, a slight misalignment can cause noise. Hopefully, with a little more tinkering, you'll silence that knock and get back to smooth cruising in your Explorer! Hi this is Dusty, I'm one of the auto experts on RepairPal's Car Genius team!