Well this is just what I was looking for! I've been having this debate with my dealer for some time now on my FR diesel. I already suggested a pulley / tensioner but they seem reluctant to pick up the spanners and have a nose about. They did blindly apply a fix from Seat to do with air intake pipes...no joy there!
It's been worse on cold mornings, but never goes away. Sounds clear at 40mph, in 4th gear then accelrate hard.
I presume this could also apply to a diesel???