1999 Stratus, 2.5L, 180k, new serp belt, alt, idler pulley in June of 2018. Idler pulley was whirring. Fixed until recently; now the belt area has a combo rattle, screech noise. Gave the serp a hit of PB Blaster and cured it for a minute, came back screeching like a hungry owl. Belt has perfect tension, might be a tad loose. How do I isolate which pulley is making the noise without replacing them all? Thanks.

 

I'm not a mechanic but maybe you could get a set of mechanic stethoscopes. I remember seeing a mechanic use one and thought friggin nice.

please let us know what happens