Hey mate, I don't have a Z750 but I have a low km 05 636 and it makes a tappety noise, but it's the cam chain tensioner, just a thought for you. I bumped into a pretty cool trick on another forum for tightening up slack chain tensioners very easily, but proceed at your own risk!
"when the engine is running the cam chain whips the tensioiner (chains don't wear evenly), which is the noise you are hearing. The spring pressure isn't enough for the tensioner to adjust to the loose part of the chain because the chain is spinning too fast....but you don't want too much spring pressure because it will wear the chain slippers prematurely....... wanna know a really easy way to adjust it...........fully warm your bike up, put it on a rear stand, put the gearbox in 6th(engine off!)....grab the rear wheel & roll it over 2-3 times...it takes some muscle, but it will allow the cam chain to turn slow enough for the tensioner to adjust to the loosest part of the chain."
That's might be a bit confusing, so in summary:
1. warm up
2. shift into 6th
3. turn motor off
4. with clutch out roll forward a few metres
Good luck
PS don't overfill the oil or you'll risk real damage to the engine