I am battling that right now on my 2001 Frontier. Used to only happen at startup on cold days. As the hummidity got more and more this summer it bacame more regular. I tried tightening the belt and that didn't help. My guess is the bearings in the pulley are bad and therefore squealing. I do shoot some oil in there and it will go away for 2 weeks to a month. THe thing that sucks is that I know what part to repair, but the dealer has to be able to recreate the problem... I think the pulleys are only about $40, so to avoid the hassle, I may just switch it out on my own...
_________________________
Jeb aka Ag Bullet
2001 Frontier S/C CC
www.nissanfrontier.net My Ride Most of the world's problems can be solved with blunt head traumas.