Unless you have x-ray vision, as Brent says, I would take the cover off that the gearlever comes through. On my car there (1995 crossflow), there is thar cover plus a larger one, but your car may be different.
While you are having a look, you could also take some of the weight of the engine on a trolley jack (But not too much), and see if there is left / right movement of the gearbox rear part.
It sounds like a propshaft UJ, or else the gearbox mounting, as others have said. Either way, I would think carefully about driving until you resolve it!