I was in my 740iL today working on fixing a number of faults with the glovebox suspension system when I noticed this odd grey coloured plastic cover plug in my passenger footwell kick panel. The one with the speaker mounted in it.

That plug there part 5 with BMW part number 51438101039 is the grey covering plug I'm talking about. You can't see the hole it covers from that diagram, because the panel isn't shown with the hole present, but it is located in the very top left corner of the panel as pictured there on RealOEM.

My question is, has anyone else come across this peculiarity before and wondered what this plug is covering up and why it is seemingly not available in the interior trim colours of the car? I thought mine had some dodgy aftermarket plug in there being as it is grey and stands out like dog's balls against the parchment interior trim colour, so I found the diagram and the part number and found it's simply not available in interior trim colours at all. The piece of plastic does not look like a BMW part at all in fact. It has no BMW roundel and no part numbers moulded into it at all, however it does indeed look exactly like the one pictured in the RealOEM diagram in terms of shape. Anyone got any ideas?