Maybe its how I am used to gasoline cars...but crusing on highway at 65 with my 240D I always hear a humming from the engine and vibration on the seats, as well as vibration the fold down armrest. Is this vibration and noise normal? When I take it to get the valves adjusted, I am gonna ahve the mechanic take a look at the driveline to make sure nothing is wrong. What you guys thing?