A belt with hardened rubber can squeal. If you have a new belt, install it and tighten to proper tension. Ensure all tensioner hardware is still there and that all pulleys are in line with one another. The remark about the balancer on the crank is spot on because it can walk over sideways as it separates. I just had a squeaking (on/off) belt on a 5.3l V8 in an Impala I changed yesterday, check the crank balancer for this condition. Sometimes and only sometimes pulleys will be so smooth from long term use, that they will squeal and cause issues permanently. What does your car idle at, and is your wire to the power steering pump hooked up?