To be honest I don't really know. All I was told was the service tech used "a lot" of felt tape in the rear hatch area and now my car has never felt or sounded so solid. The rear hatch itself can still move from time to time over certain bumps but there's no more trim panel vibrations anywhere. 1500 - 1800 rpm cruising use to have a low level vibration that is no longer present and my annoying rattle coming from behind the driver's side seatbelt area is also gone. My car feels like it's carved from a single chunk of metal now which is really nice!what was this part they corrected, I have that same annoying rattle at low RPM's.