i have heard of this issue...i personally have not seen it. I have hear that drilling a small hole in the throttle body blade will fix it. I believe something as small as 3/16 or 5/16 will do the trick.
Do some searching...i know this topic has been covered before. good luck man.
My 94-95 style throttle body doesn't whistle, but that doesn't mean the Fox style ones don't. The biggest issues I've heard of with the Pro Products throttle bodies is the butterfly sticks for some people. I've been fortunate that I don't have that issue, but it's a valid concern to be aware of when shopping around.