My 2009 A4 with the 2.0T and the CVT just started making a whistling noise at idle. As soon as I open the throttle it goes away but as soon as it closes, the whistle comes back. It even stays for about 10-15 seconds after the engine is shut off and occasionally I will get a CEL at idle and a code for a lean condition. I monitored the A/F ratio with Torque and it never went above 15 at idle.

The noise is definitely coming from the top of the engine, seems to be around the throttle body which I would have figured was a diverter issue but there shouldn't be any boost pressure at idle, right?

If anyone has any ideas I'd be glad to hear them because I don't know where to start.