The squeal from hell!!

Hello all, 99 Tahoe LS 5.7 4dr. Went through car wash now the motor is screaming. The shop has changed out the idler pulley, belt tension pulley, alternator, and 3 different belts. It sounds like it is coming from below but they say they can't locate it. 400.00 dollars and still no help but the new parts look nice... Suggestions are appreciated!!

Squeel follow engine RPM? How about load on alternator?

Make squeel with belt removed? How do the bearings in alternator feel? Bearings in AC Compressor?

you mentioned the tensioner pulley but not the tensioner itself....are we sure there is enough belt tension and no binding spots in the tensioner travel?....