I've been driving it all day like this and haven’t noticed any sort of noise that could be considered "whistling" but I've been told that the manufactures use resonators on the intakes to help cancel out intake noise that regular vehicle owners might find offensive. For those of us running headers and modified exhausts - it's just a waste. Fact is Ford Racing sells the same CAI without the Kidneys.

What was the purpose of the stock "kidneys"?