I have a 2004 Durango Limited with the 5.7 hemi and 4wd. All of a sudden I started hearing a rattling noise coming from the engine. Sounds like valves tapping. It stays constant with a slight increase when I rev the engine, but quiets down when the engine idles down. I have no loss of performance. I took the belt off and started the engine for a second and the sound was gone.Leading me to believe it was a pulley. I checked them all for play and tightness but they all seem fine. I put the belt back on and tried listening to them through a pry bar and the sound was consistent with each one. How do I find the bad pulley with out replacing each on with a trial and error?

 

The lower idler pully on my 5.7 exploded one day with little to no warning. Literally disintegrated leaving only the rear half of the bearing on the bolt. This was at 120,000 miles.

As I recall, both idlers were around $10 or $15 a piece. Easy fixes, once I got all the shrapnel and bits of belt out of the engine bay.

I'd start there and replace them both. Cheap, easy insurance.

Next step would be to spray each pully with some good grease while the engine is running. Just a quick shot on the one that's bad will quiet it down. Yes, you'll have to replace the belt afterwards, but a little shot of grease on the bearings won't do any damage anywhere else.