weird and very extreme vibration B180 w246.. please help
 

Hi Folks,

help please with my w246, I'm greeting a very extreme vibration that cause the whole car to keep shaking suddenly while on soft acceleration and it goes away if I accelerate hard.
it has no specific pattern to occur, it comes and goes out of no specific reason meaning sometimes it never happens and sometimes it happens.
visited a workshop and they said it's because of the transmission, although the transmission fluid was changed along with the filter recently.
as well they said that the oil levels in the transmission is good and the oil looks ok however there is a burn smell and they are suspecting the clutch and said u will need to replace the transmission... I don't trust them and I'm confused how could be the transmission needs to be replaced although the car accelerates perfectly and no issues with the shifts and as well no single error message.

worth mentioning that I've replaced recently as well the transmission mounts and that on e of my engine mounts as well need a change.

just to clarify the vibration feel .. it's pretty similar to the vibration when the car is running on 3 cylinders only and not four... could it be the spark plugs !!

again it's not continuous it just comes and goes .... please please help if any has similar symptoms

Clarification
 

Found the below post which seems describing the same issue
when the engine is not under stress (ie cruising) a vibration sets up which gets worse if you do nothing. Changing the engine revs by decelerating or accelerating, or shifting gear manually, stops it until you get to that "sweet spot" again. It makes motorway driving quite difficult.



Thanks in advance!