I understand many Avalons have this squeaking noise.

The fix maybe is squirting some silicone between the windshield and the rubber molding on the driver's side. One needs to lift up the rubber slightly with something thin that does not scratch the windshield and squirt a little silicone into the area.

Inside or out?

I applied the silicone to the outside of the car, but I notice today that some of the squeak is coming back. Hopefully more silicone will work as my can running out at time of application.

If the seal is actually beginning to squeak, it more than likely needs to be replaced.