i had a belt squeal on my caravan that drove me nutz,,,,,,,,,,
replaced all the pulleys and the tensioner. also used the gates belt.
checked pulley alignment, bearings in the water pump, alternator, and power steering pump. all were good.
as a last resort, i spritzed the belt while running with one of those belt quiet sprays, and to my amazement, it has been quiet for over a year and a half.
i have no clue why those spritzes worked, as the belt was not glazed, nor were any of the pulleys. so who knows ?