Thanks for all the replies. It's definitely not a frozen caliper. I wrapped a bungie cord around the front of the roof rack and it seems to have diminished the noise. Had other 740s with roof racks and never heard that sound before!

I had a 740 sedan that developed an annoying noise that was much like the sound I made as a kid using a piece of broad grass blade. Sort of stretched the grass between my upright thumbs and blew across it with my mount.

It turned out to be the stainless trim around the windshield. I eliminated it by pushing a piece of flexible plastic (parking pass that hangs from rear view mirror) under the trim at the top where the wind was causing the trim to vibrate.

Randy

After a trip, check the wheel centers for a hot one - be careful, it could be really hot - the sign of a dragging brake caliper.

When empty, our clamp-on roof racks on our 850s made noises, as fit the factory rack on our 745s when certain loads and ropes were used.

From your description--it does sound like roof rack noise -- but there's a possibility it could be the driveshaft center support bearing. Temporarily removing the rack may not be practical - although if it's mounted like the 240 racks it's a pretty simple thing to do.
The old original VW beetle used a clamped down rack that was particularly annoying with wind noise. -- Dave