I thought about telling the OP about that, but it was mostly just a 700 issue. My '89 developed that problem at highway speeds. You could identify the area by selective use of taping various areas of trim, usually the upper area of the side moulding strip. Volvo actually had a TSB about vibrating/whistling windshield trim in 700s. As I recall, for customers who came in to complain about it, the fix was to slip a trim tool under the moulding at the mounting points shown in a diagram and turn (counterclockwise?) the square plastic mounting clip a bit so the plastic fingers stuck out properly to grab under the lip of the moulding. By the time I read that, I'd already shot silicone sealant underneath to end the problem.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now