Cannot find my original post so reposting. I have a newly acquired 2005 Outback LL Bean wagon with 225,000 miles. Just noticed a horrible high-piched chirp coming from either the rear wheels or rear differential only when backing up. Touching brakes has no effect. It literally sounds like a couple of seagulls chirping. Just got the car from a dealer and original owner babied the car---I saw the records. Any thoughts?? Quick diagnostics?? Thanks in advance.