it is the idle air motor ports.....
the back port is a huge chamber that then has a hole that goes into the actual throttle area....if you fill up that chamber so it is just a hole it will stop whistling....
I did this on mine after trying all the othe sugestions of drilling the plate , chamfering the holes etc.....this worked great.....if illed it with a thick pice of rubber with a hole drilled in it.
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