Rattling Octavia

I have an Octavia L&K with a rattle/clunk which seemingly comes from the drivers door although rattles being what they are I can't rule out A post or B post etc.

Even braking or accelerating makes is go clunk as does the slightest road imperfection. The dealer has had it in twice but no joy. I took the wheelarch liner off and a large lump of foam fell out but I can't see where it should go or find anything in there that is rattling.

Any suggestions welcome - the noise is driving me b***** mad!

Paul B