XSeries-forum

Any ideas what this could be? 

Seems to be a stationary or low speed vibration/rattle that has a slightly metallic sound to it.  Coming from the engine bay, if I had to guess I would say more on the drivers side.    If the car were a manual I would suspect it was something to do with the clutch.

I only bought the car a couple of months ago and I've barely driven it, so it might just be a characteristic of the diesel engine that I have only just noticed.  My last car was a petrol and obviously diesels rattle more.

Bit worried it could be the gearbox?  Are these engines known to be a bit tractor like at idle?

Being a 6-cyl they don't normally sound 'agricultural' at idle.  If it's at the back of the bay it might be the torque converter but that would be audible on both sides.  It is a known weakness..

Slack timing chain is a possible, though rare and at the front.  Loose engine shields?

Try finding someone else locally with a known good car and see if it's the same....