Some of the 3rd Gen Z1000/Ninja1000 make a rattle noise at cold start when the clutch is disengaged (lever pulled in).
I believe that the noise is caused by the clutch plates being dry and rattling against the clutch hub/basket.
Here is a video of the noise.
2011 Z1000 clutch noise - YouTube
When I removed the clutch plates from that bike the plates were very dry, normally they are coated with oil.
After the modification the owner said that the clutch was smoother and the noise is gone.
Here is the modification.
1st - Remove the clutch plates, make sure to keep them in order.
2nd - Remove the clutch hub.
3rd - you will want to use a 1/8 inch drill bit to drill holes in the clutch hub.
You have to be careful not to drill into the spring bosses and the webbing that is used to strengthen the clutch hub.
Notice that the holes go over and up and after the 4th hole you will start over at the bottom.
I had to skip 2 holes because they would have gone into the webbing.
The new holes in the clutch hub allows the oil that gets into the center of the clutch hub to get into the clutch plates better but we still need to supply some additional oil into the center of the clutch hub.
This picture is an exaggerated example of the flat that you will need to grind on the clutch release rod.
The diameter of the shaft is .417+/-
You will want to grind a .010 flat.
Now using a service manual reassemble the clutch assembly.
I use and recommend Yamalube 10w-40 conventional motor oil.
I plan to do this mod to my bike and when I do I will get some photos of the operation.