Clutch noise 99 ranger

When letting out the clutch while starting out in first gear, there is a low pitched squealing noise that i can hear after the clutch has engaged and the truck starts moving forward. sort of like a wuuuuurrrppppp noise. it only does it when the engine is cold and will do it for about the first five or six stop signs on my way to work and then it quits. it also will do it sometimes when i down shift. I noticed it within the first week after i bought my truck last year and took it back to the dealership. they said since the clutch was functioning, they weren't going to do anything. it also seems to be worse after it has been raining overnight, and it is alot worse when moving from a dead stop up a hill. Any ideas as to what the problem might be? the dealership said the solution was to replace the clutch, but i want to make sure that is the solution before i have it done. thanks for your help!