The idler pulley was replaced I believe, w/ the one from the ASP 178 kit. How do you check it out? What do I look for?

When you started hearing that high pitched sound when did you hear it, at idle or at a certain rpm like me?

PS It won't make that noise in Park regardless of RPM, only: 1. While in drive 2. With moderate throttle input and 3. Between the aforementioned rpm ranges.