Had a squealing belt until now. It was definitely too tight, according to the 90 degree/white thumb rule. I adjusted it, aligned the wheel, tightened things up and took it for a spin. Acceleration ..noiseless. Deceleration: big howling sound. Probable cause: too much slack?
Adjusted again, just half a turn on each bolt.

New spin: acceleration dead quiet, deceleration: just a faint sound of things moving, not the protesting howl from before.

I got it right the 2nd time, didn´t I?