Balloon rubbing sound coming from where dashboard meets windshield, at highway speeds??

This time of year PC gets a few posts on creaks and rattles on the G3s. Welcome to the club! I plan to pull my dash out completely (again) and go over it with felting and silicon gel lubricant where plastic meets plastic. Almost all of the plastic interiors are assembled with "stab-lock" connectors. If the fit isn't absolutely perfect, and over time, these connectors will abrade with each other and you will get creaks and rattles.

To address your issue (if you are lucky), it could just be the edge of the main dash plate rubbing on the base of the windshield itself. One member here sprayed WD-40 between the two and solved it. Since WD-40 has some petroleum as a component, it could cause deterioration of the plastic. I would suggest getting a spray silicon lubricant such as "Blaster" from Home Depot. Silicon on plastic is OK. My trick is to extend the wand. If you have some extra wands from other products, you can put them together (I use 3) with about 1/2 inch of 12 gauge wire insulation between the wands. You just put the wands together using the insulation as couplings for one really long wand. Now you have better control and can get the lubricant directly into the area between the base of the glass and the dash plate minimizing the overspray. Go easy on the spray button to control it. A little goes a long way. With your fingers, move the dash plate down a bit to allow the silicon to work its way between the 2 surfaces. If this was in fact your problem, the noise should stop. If not, the problem is deeper in the dash.