I understand what everyone is saying about older belt needing replaced, and scuffing the pulleys before putting a new belt on.
But I still dont buy it. I dont think its a coincidence that it only seems to be Ford F-150's I hear. I live in AZ and we NEVER have condensation issues. Plus Fords shift at lower RPM's then GM trucks when you floor it, and I never hear a belt squeek. I think there is a design flaw in the pulley system.
And why on shifts where the RPM's drop instead of increase? I would think it would be a downshift where it squeeks, not an upshift.
Hi ya'll. New here. Came across this post and I would like to say that I am having the same problem and I live here in the Atlanta area. I drive a 2000 Ford Ranger XLT Ext Cab. 3.0L Flex Fuel addition. On humid days and especially humid cold days my truck chirps. Boy does it ever. It goes away when the day warms up or I run the truck for a while to dry out the belt. I belive its the belt. I just replaced the belt with a gatorback last summer. I thought it might be my idler pulley seeing the noise seems to be coming from that area so last week I bought a new one and put it on and it came right back. On humid mornings I can hear it from inside the truck man it unbearable. I don't know what to do. I don't belive its my tensioner because I had that looked at and its pretty good tight. Only 43,000 miles on this truck and its babied. I don't know what to do. I guess I could try buying a dayco belt next and see if that helps. But if the gatorback is doing it i don't think the dayco is going to make a difference.