Knocking/Clicking noise 1.8T

[LauMorgs]

I am really baffled as to what this noise is! It sounds as though it's coming from the turbo area.. It's kind of a rapid clicking/knocking noise, it disappears after a little while but then randomly comes back.
Nothing is knocking externally that I can hear, tried wiggling things & applying pressure on things but nothing quietens it.
Thought that it might of been heat sheild but ruled that out.
Can only really hear it when the car is just ticking over, it seems to disappear once the car goes over a certain amount of revs.
Can anybody shed any light on what it could be if you've had similar problems?