94 1500 4x4 Squeak/Rattle

[BigbadBill4x4]

I have a 1994 Chevy 1500 4x4 with 5.7.Lately when I start after a couple of days,serpentine belt squeaks and has actually walked off the idler.Last couple of days while doing this,it has started making a rattling/clattering sound and then clears up.If I shut it off and restart multiple times,problem does not reappear.This only happens after sitting for a couple of days.I have checked all pulleys and have replaced pulley on tensioner.All pulleys seem to be ok with no play or roughness/squeaking.Thanks