Thanks for all the great feedback. We think we finally located the problem. We checked all the hatches, vents, antenna and awning. We found that the front awning arm is not seating snugly when the awning is rolled up and locked into position for traveling. It's a Dometic awning. The rear arm sits snugly. When there is a strong crosswind, it causes the arm to rattle. I would've sworn the noise was emanating from above the windshield and I'm not sure why we seem to hear it more there than through the side door closest to where the arm is actually located, for example. Nonetheless, we are convinced (or perhaps extremely hopeful) that if we get it fixed we will be rattle free again.
Thanks again for all the helpful suggestions. The responses here caused us to stop focusing on the structure and look at the exterior component parts.
