Some odd noise in my tank :s

[martinblueprint]

I posted this over at 197.net too, but thought maybe someone here might know.

Basically, trying to track down the knocking noise in my 197, I noticed there's something rattling about in my fuel tank...

[video=youtube_share;MbZiBlFsTlc]http://youtu.be/MbZiBlFsTlc[/video]

Anyone have the foggiest what this noise is? Like a ball in the bottom of it?

 

[Bodge!]

Fuel sender?
Or fuel level indicator?

 

[martinblueprint]

Yeah perhaps. Should it be making this noise though if those are the culprits? Seems like they should be fixed down at least?