Mystery Squeal

My '06 SR5 (77K mi.)has developed a squeal related to the serpentine belt area. I'm not sure if it's the belt, pulley, alternator etc.
The alt. has been replaced a year ago.
On the fist start-up of the day the wetter out out it has been (rain,heavy dew,humidity) the more it squeals,if it is dry and sunny,there is no noise. If I warm (idle) the truck up the noise eventually goes away.
Belt tension seems OK but I will check it again.
I'm leaning towards the idler pulley as the culprit but it is hard to pinpoint.
Any suggestions,tips and help is appreciated.

John

 

Buy a new belt, first and see what happens.

 

Yeah,I was hoping to not just throw parts at it until the noise stops but that seems like the place to start.I should have said that I have already had to replace the belt 5 times.Seems to be a weak point,any suggestions on a good belt (brand).

 

Could be waterpump. Easy to check....with engine off & facing engine....grab the top fan blade and pull it towards you then push back if it wobbles like it's loose the bearing is going bad. Bad bearing will squeal like that when 1st started.

 

$0.00 tip courtesy of Hot Rod Magazine: baby powder will silence a sqeaky belt.

 

...and a squeaky wood floor...