I have a 1.8T Mk 4 with 60,000 on the clock
It had the diesely rattle at start up - worse after being left for a while
My local dealer (Lindvale Southend) diagnosed it as being the cam chain
tensioner not retaining oil pressure.
They changed it under warranty ( I just sneaked in on the time and
mileage limits).
Now it is much better and seems to run a lot smoother too although
that might be the BP Ultimate gas. Third tank full -expensive but good.