Mr Onion, I had a rattle and it appeared to come from the N/S/R seat hinge. I looked it all up in the online manual and quite honestly balked at the removal of the tray etc. I managed to get the hinge out without removing this cover.
Can you not find a way around removal of the cover as there is every chance not only might you break the very fragile clips that Honda use moulded into everything but you will not get the cover back as they did in the factory.PS the seats are VERY heavy and 'B' awkward to move around, which you will have to do to remove anything underneath.
Good luck and reading the online manual will give you all the info you need