The side panels on the stalker are 0.065 inch thick aluminum held with a few fasteners at the front and rear ends of the panel. There are flanges bent in at the top and bottom, so the panel is fairly stiff along its length. But from top to bottom it can flex, which allows it to bang into the vertical legs of the frame. My Stalker demonstrated by having an incredibly annoying buzz from the right side panel when the engine was near 3500RPM.
The fix was simple, if a bit time consuming. I spent some time search through McMaster-Carr (sometimes their prices are a bit high, but their online catalog is worth supporting) for some single sided foam tape and found this Neoprene rubber strip (8694K68).
I pulled the side panels and applied this tape along all of the square frame components, and beneath the diamond plate flooring.
This was very simple, inexpensive and only added about 1 pound to the car.