I think I'm having the same problem with my K&N drop in with the stock intake and resonator. It happens sometimes at startup/idle, and in the low RPM range (when rolling around a praking lot etc.). I plan to put the the stock filter back in to see if it goes away.

Do you all think that cleaning the Throttle Body may alleviate the whistling problem we're all having? It seems as though these intakes are only amplifying a noise we normally can't hear :dunno: