The wind won't be as loud with the top up
lol sorry I couldn't help myself. I don't have a roadster, but my Craftsquare mirrors whistle pretty loudly in certain conditions. It varies mostly based on my speed combined with the atmosphere wind speed/direction. I'm guessing yours is more of a constant hiss or does it vary with speed? First thing I think I'd check is to make sure the top is fully seated when stored.