On Saturday as I was leaving work I had to bump start my bike, on my own, fun.

The starter solenoid was just clicking and sending no power to the starter motor.

Then when I got home I decided to see if it'd work again and lo and behold it did.

It was also fine yesterday but I decided to have a gander at it.

I took it out of it's boot and everything looked fine, all connections were clean and tight etc but when I shook it something rattled around inside. Is this normal?

Sometimes the contacts burn inside them, the rattle is prob the solenoid iron rod, can you get it to bits? I've cant remember if there rebuildable. There was a guy who was selling solid state ones on here but never replied to my email.
Have you put a meter on the output with the starter button pressed to make sure it not the starter motor that's blown?

It's working fine now, it's just I can hear something rattling round inside it.

Maybe a new one as a precaution?

They will rattle its just the solenoid core/actuator moving up and down. But if you can't get it to bits I'd buy a new one.