Ah, I get it. Well, I have the flat area that is under the pin box down far enough to peer into where the pin box is attached to the frame, and cannot see any damage, broken welds, etc. The front cross member that supports the sheet metal is (I think) wood- wonder if there is some rot there, causing the sheet metal to flap in the breeze, and that is the movement that I am seeing? Hope so- I will peel more sheet metal before declaring the war over, but I would much rather replace a piece of 2x2 than call in a welder!