The serpentine belt has a drive side and an idle side. The drive side is ribbed and is used for the high load components comprising the crankshaft drive pulley, alternator, power steering pump and A/C compressor. The idle side is smooth and powers the water pump, idler wheel and tensioner wheel. The belt itself is not likely the problem provided the tensioner is working properly.
You probably put soap on the smooth side of the belt and since this affected the noise, then I would say you need to look at the components that are directly affected: idler, tensioner and water pump.
The tensioner is under a lot of spring pressure so test that first. You need a long bar and 15 mm socket to release the tension and it should snap back very strongly. If not then it is not right and needs to be fixed. If it is OK, then you need to remove the belt and recheck the bearings on the tensioner and idler pulleys and the water pump bearings.
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Art
2000 Taurus SEL Wagon 3.0 Vulcan (daily driver)
1993 Taurus GL Wagon 3.8 Essex
1991 Mercury Grand Marquis LS 5.0
1986 Chevrolet 3/4 ton pickup 4x4 350 with turbo400 and 208 transfer case
1978 Chevrolet 3/4 ton pickup 4x4 custom 6.2 na diesel with turbo400 and 203 transfer case
Planning 2008 Taurus X in a year
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