engine noise

[rip_mr3]

I have a 2004 explorer 4.0 engine, it has a rattling noise in the front bottom part of the engine, to me it sounds like a ball bearing spining fast, can anybody tell me what it could be??? it only does it at idle

 

[Rick]

Possibly a bad bearing in one of your accessory pulleys. Take off the serpentine belt and listen and feel for roughness in the bearings.