2000 Hyundai Accent Cold Weather Power Steering Squeal at s

Bought the car Sept 2007 with 56K miles in November on cold days the belt would squeal at startup would go away after warming up just a little, the colder it got the longer the squeal. I changed the 2 belts in November (has power steering, alternator, water pump) Still had problem, in Dec 2007 had Timing belt replaced (59,000 miles) by my very experienced mechanic. Told him about the squeal weather was warmer and he did not do anything for the noise just changed timing belt and readjusted other belts. Tried sucking out fluid with 2 to 4 ounces at a time and and then replacing that amount at power steering fill tank. Did this about once a week until had exchanged one quart of quality Power Steering Fluid. Believe it got a little better but when in teen's (degrees F) or even in the low 30's squealed last winter. This winter still noisy in cold even after taking out 8 ounces during the summer of power steering fluid and putting in a fixer that has helped in the past with other older model cars that I owned. Do not believe air is in system, belt is good, could it be the filter in the bottom of power steering fill tank. Squeals at startup on cold days, do not even have to turn wheels, of course turning the wheels squeals worse on cold days, when warmed up car steers excellently and quietly.