I use meguiers as well and I get the streaks, but before I ever used meguiers I didn't see the streaks. I think it is just water running down the side from the screw holes because I also get streaks in other areas where there are no screws, like on the back in random places.
I don't know if that helps, but I think it's just the water running down and streaking the meguiers coating on the cladding.