Location: Mount Aukum, CA - El Dorado County about 55 mins from the Rubicon Trail
Do you have an aftermarket intake or performance throttle body. A lot of times aftermarket TBs have casting issues in the throat that cause a whistle. Air intakes will do it just from the volume of air moving through the opening.
You just take a can of carb cleaner and spray little bursts around vacuum lines with the engine running. If you find a leak, the rpm will change. This helps you pinpoint exactly where it is so you can deal with it.
I put on a Banks cold air intake thinking this may correct the problem but it didn't. I believe the Throttle body is stock. Not sure how to check for leaks.
My CAI only whistles when its cold then goes away when warms up. Is there a spacer between the TB and the Intake Manifold? TB Spacers can cause the whistling also. I would make sure to eliminate the obvious and easy things first.