Hello, Have a Mercedes vito 112cdi w638 bj2001 with 404 000km My question… If I drive in the 5th 50 km h it makes 1200-1300rpm You have no vibrations, engine becomes much quieter.. If I then settle from 50 to 65 (in the 5th) it makes such a suction-like noise Is that healthy for the engine or should I rather drive with the 4th and that 1500rpm(at 50km h)? Lg