The passenger vent window on my 68 whistles when all the windows are closed and I get above 30mph.

I made sure that the window is tucked inside the rubber.

Not a problem when the windows are rolled down. And I know one answer is to turn up the stereo.

But it drives my crazy. How do I fix this problem.

Thanks in advance for the help.

replace the vent window gasket.... No kidding.. I use to use my 56 el camino vent whistel as a speed indacator,, the fast you go the hight in pitch it went.. a new set of Metro Vent gaskets fixed it up...