Hello

I've got a GS500 which makes a rattling noise at tickover, I think I've probably done 20k miles with it like that, not really worrying as I haven't noticed it getting any worse and don't have the time to strip the engine down if it is something major.

Tilting the bike sideways with the engine running doesn't silence it as something I've read suggested it should. If I go around the engine with an extension bar as a stethoscope, I hear the noise best when listening to the sides of the inlet camshaft.

Video.

Whats the verdict? Does this sound like harmless camshaft endfloat or something more serious?

Ermmm, can't say for sure by the video. sounds like rod knock. my GS did sorta the same thing, the "noise" would seem to "go away" with REVs and it was a dead connecting rod bearing. that eventually got so small it spun on the crankshaft. then my bike made a REAL horrid noise, and stopped. think marbles inside the engine. 

if its rod knock, go ahead and buy another used engine - sell the good parts on yours to try to recoup most of the cost. I rebuilt mine just because I wanted too.

The cam shaft noise will distinctly be upper end, and that stethoscope method is pretty accurate, but check the cam shaft for end play.
If its anything over .3mm it will be making a tapping noise.
Cool.
Buddha.