I had this. They clip a weight or something on to the wastegate rod. This is the US so different but it's the same sorta fix:
http://www.golfmk6.com/forums/showthread.php?t=20401This might be the UK info:
The Bulletin reference is : 2021062/7 Dated: 18.08.11.. (Latest: 2021062/12, 12 Dec. 2012)
"Engine - rattling noises from engine exhaust system"
Fits the same part as the USA instructions in the 1st post. Part Number: 06J 145 220A
Problem:
Rattling or jarring noise from the area engine compartment/exhaust system occurs between 1900 and 2900 rpm.
Cause:
Because of exhaust gas pulsations, the flap and rods of the wastegate vibrate at the start of the boost air control, which causes rattling or jarring noises.
Solution:
Fit a spring clip on the wastegate adjustment.
Part:
06J 145 220A – Spring Clip.
Warranty:
Claim instructions are incorporated for dealer claim.