Rattle on startup

[selecw]

When I press the starter after the bike has been standing for a while there is a rattle. It stops as soon as the engine is running.

If I turn the bike off and start it again, there is no rattle.

What is it? I thought maybe insufficient battery power to turn the starter.

[FJmonkey]

Starter chain, get over it, our air cooled lumps rattle... Welcome to the club...