you might want to try some "belt dressing" It comes in a can that looks like spray paint. I dont know exactly what it does or how it works but I would assume it just adds some friction to the pulley and belt surfaces.
Might have something to do with the pullies being aluminum and not steel. The anodizing could be smoother than a regular steel pulley, therefore lower friction and relative slip, and squeal.
Dont use a smaller belt or max out the tensioners, all you will do is overload the bearings in your alt/ps pump/AC pump, and you'll end up with a whole new set of problems.
Im pretty sure this was the stuff I used before,
http://www.valvoline.com/pages...ct=32