2.0CRDI vibration when engine is shut off

Hi all, 
Recently I've been noticing that sometimes when I turn the engine off, I am presented with a short but powerful vibration (coming from the engine bay). I do not hear any rattle or anything really, but it gives the car a good shake that can be easily felt. Unfortunately the issue is quite sporadic: sometimes does it for a week, then skips it for a week or two. 
As luck would have it, when I had my mechanic take a look at it it was good as new... The car is a 2013 estate with DSG and the 2.0CRDI engine, 270k kms. 
Any ideas? 

PS: slightly off topic, but I don't really want to open a thread just for this. I'm considering replacing my trusty old superb, but it really has no significant issues that would make the change worth it. What issues can I reasonably expect in the say, next 50k kms according to your experience? 
 

Thanks a lot as always!