Since it has gotten colder in my area, I know your belts would squeal due to frost. But in my case after being warmed up and driven about 3 miles to work and I downshift, and one of my belts begins to squeal. I do have the Perrin Lightweight crank pulley. It was done correctly I did it 3 months ago, and replaced my belts along with the small A/C tensioner pulley as well. Never had any sort of sounds until 2 weeks ago and its a squealer for about 4-10 seconds at a time even with the heater/blower off. I've got the alternator tensioner adjuster as far as it would go but the belt tension is still within reason not loose not super-tight. And in some instances it does it on normal Daily Driving take off's.
Any insight is appreciated.