Well, I have never seen a car with one of those valves. It appears from the parts film to be a decel valve. It is teed into the inlet and outlet hose of the aux air valve with a vacuum line going to a third port. Based solely on the place of installation I would say that it is intended to add air on decel either for emissions or idle stabilization.
I don't suppose it should rattle, but if you plugged all three ports it would work like most 110 engines worked and eliminate any problem that you think it might cause.
Bosch Master, ASE Master, L1
33 years MB technician