Rattling noise under hood

[tejano01]

Got a 2000 Ford Mustang GT with 137K + miles on it. About 3-4K miles ago, it started developing a rattling noise under the hood. It looks like it's coming from the belt area.... can pulleys go bad on a car? And if so...how big a deal is it to replace pulleys... I have attached a video... any advice would be appreciated.

YouTube - 2000 Ford Mustang GT

 

[trinity_gt]

Idler pulley and tensioner problems are not that uncommon but I believe you're going to find the problem is related to the timing chain tensioner or guides.

And easy way to tell is to simply remove the serpentine belt and start the car. If the sound remains it's not anything associated with the belt, idlers, tensioner or accessories. That leaves what's going on behind the timing chain cover as the most likely suspect.