All my Kayfuns whistled....drives you mental. What's the lowest resistance an mvp will fire....1.2 isn't it?
mvp will fire down to .8. the whistle is caused by the air passing over the air hole fast, the only way
i cured mine was to drill a countersunk hole around the edge of the standard air hole.
just get a drill bit thats larger than the air hole and gently take the edge away, cured all of mine.
i build a 1.0 1.2 ohm coil arond a 2.5 or 3mm bit with 28 awg wire, maybe 6 or so wraps.
i use one every day at work on an mvp and this works great for me.