2010 800GS - Rattle in fuel tank !

Hope somebody can help me solve the rattle we have picked up on my wife's 800GS.
We did a very bad dirt road section around the dam in Wakkerstroom recently and seemed to pick up an annoying rattle in the fuel tank area !

I have looked up all the fuel related posts but cant seem to find a similar problem reported before.
Anybody got a bit of info on this before I open the tank and start removing the pump etc ?
Seems to be around the fuel cap area..

Thank you in advance.