my gpz500s is making a weird sound?

The word "still" in your question leads me to guess the problem was there before the head change, any background as to what made you suspect the head? Couple of checks listed below for you to try.
Coils and suppressor caps ok?
Double and triple check you have the valve timing spot on, one of your cams could be a tooth or so out.
If that's correct (and I'm assuming you have new air filter and plugs fitted) it could be fuel trouble, is it running on both cylinders all or some of the time? Try.. Cleaning the petrol tap, filter and carbs, while you're in the carbs check all the "O" rings and diaphragms, check the needles and jets for wear. Next, try balancing your carbs, carbs way out of balance can cause the bike to be lumpy

Duncan
May 2008

Have u done a compression test?

Debbi
April 2008