TD5 fuel pump whirring

Hey up.
Disco 2 TD5 fuel pump was singing like a good un, no loss of power or anything just the noise was driving me crackers.
Took out the pump from the tank, the plastic mesh filter was covered in black felt like crap.
Got the missus to clean it all off and reassembled, running fine now.
Dead easy to do, the tricky bit is getting the interior out and back in.
Has anyone come across this black stuff before?
If it is microbiological growth will it come back?

Fatmatt.

Could be diesel bug.common in marine fuel systems.you can get a chemical to treat.
DIESEL FUEL BUG

It can also be caused by leaking fuel injectors that allow diesel to leak back to the the fuel tank.

Micro biological growth would be through the entire fuel system and would cause running problems as it would block the fuel lines and injectors, it grows in fuel that has water contamination and looks like snot so I don't think you have it in your tank.

Like biglad sayes it could be the injector seals leaking and the black stuff will be carbon from the combustion gases getting into the fuel.

Just had the little sod out again, clean as a whistle.
Just popped some aviation fuel in there from a mate.
Apparently the ice inhibitor thats present in aviation fuel also works as a MBG inhibitor.
so I'll see what happens over the coming months.