Have you checked your Tool Tray Base as the sensation may be the Differential Bellhousing Top whacking on the 'Jack' locted in the plastic Tool Tray as mine used to do before fitting a Shaped Aluminium one?
Take the tray out and see if the Spring Tops Rear Ends have been hitting the Rear Holes in the Wood Frame or not as that is a good indicator of how much movement you are getting.
There was no sign of any hitting of wood on mine but a big hole developing in the Tool Tray.
Frank
