So if you used a stethoscope that was at idle..... and at a higher vacuum level than at cruise. You probably know this: the PCV has a low flow and high flow setting that varies with vacuum. If you are using a stock Mopar replacement, then they seem to open from low to high flow at around 13-14 in vacuum. So it almost seems to be whistling at both flow settings: at higher vacuum/low flow at idle for your stethescope test, and then at medium vacuum/high flow settings when cruising.
That seems to point to the connections on the PVC rather than the internals where the variable valve is. So no hose collapsing? Are you using proper PCV hose that is made to resist collapsing under vacuum conditions?
Not sure this helps....