Several years ago I read on this forum that some people had issues with the latch whistling at highway speeeds. One person said that he turned the cap so the latch was in a different position and the whistle went away. I did not experience this problem with mine.
Also, I did almost the same thing that Pete did, but I drilled and tapped the base so the cap can't be turned at all. I also backed my cap off of the base a couple turns so that my mustang gas cap fits under it without any issues. I have a MKIII version though. You'll be surprised how many people will mess with that darn cap when they are checking out your car. They don't even know if it will hit the body when they open it, yet people who would never touch anything else will open that cap. It's like it's calling them over (like Lord of the Rings or something). I recommend where ever you put it that you make sure that none of the parts can ever touch the body.
Wibby