I doubt if anyone can tell you anything about the mechanical noise your engine is making without a bit more diagnostic work at your end - WE can't hear your noise. I think that the 16V does not have hydraulic lifters, and the other one maybe does, but I don't think this should make a big difference inside with the doors and windows closed. Is the hood pad missing?

The exhaust will not reduce the exhaust flow, if you want the engine to run. It is designed to reduce the noise w/o reducing the exhaust flow. Some exhausts will provide more resistance to exhaust flow than others, which will reduce engine performance at higher rpms, but be quieter. If the exhaust you installed was aftermarket - and not an oem replacement for MB - you may indeed get more noise than stock.

Steve