this is common.. happened on my 95 Z and from day one on my 2002 Z.. both had T-tops.. Either way.. even at 150 there is nothing bad.. I find that wind conditions make it more noticable.. see, its like a vacuum that forms.. but if the wind is still or going in the right direction, the air traveling around the car is doing what its supposed to.. planting the car and pushing in all around.. but if I were to change lanes at 120-150 then the wind around my car changes and starts to pull on one or both the windows.. causeing loud noise.. I dotn worry about it since I have done it so many times and it never seems to be enough to cause damage.. just loud..