So with the top up or down there is a distinct wind whistle. Coming from like maybe the windshield wiper area? Gahghhhh! It's annoying. Only happens around 50 mph.
If the level of the hood is not correct with respect to the front bumper cover you can get a whistling, it typically happens if the hood sticks up over the bumper cover. Since it happens both with the top up and down it may be a culprit. Here is a couple of threads that describe how to check and adjust for that:
That's why his search didn't turn up results. Had he looked for "whistling sound when I drive way too slow" he would have found out that the problem is fixed at 150mph.