I started the car this morning to warm it up for my wife and, while I waited, popped the hood. It's really hard to isolate the source of the noise but it is strongest near the throttle body. Loosening the oil fill cap causes the air-oil separator to wheeze a bit and RPM to change. Removing the vacuum line from the front side of the air-oil separator causes the RPM to change drastically of course.
So, what's my next step? I don't want to blindly start replacing parts here if I can avoid it.
