I have a rattle type noise in the engine of a Kawasaki Voyager 12

need to search for rattle -use a rubber mallet to tap frame in different areas for noise ---or if engine rattle low oil burnt damage valve -valve train

Ed, that is a tough one to diagnose from here, possible bad U joint on drive shaft, loose exhaust baffle if in the area, best to take it into a reputable shop and have them diagnose and estimate repair.
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it may be experiencing starving for oil. If it shows up after longer ride or hard stint, oil pressure's going down and the upper valve train is the first to suffer. The oil out of the breather is called "blow by", compression seeping past the combustion chamber into the crankcase, another sign of a tired engine. Be sure you're using the correct viscosity oil, a temp alternative is run the heaviest oil you can.

replace the timing belt and every thing in the front like waterpump pulleys oil seal the whole 9 yards it's time

Check to see if you have a blown exhaust gasket.

Check fluid level first, but if you were hearing rattling, it might be too late to fix with just fluid.

fan belts don't make noise, but the pulleys they are connected to can make the noise you describe.

I wish you luck on fixing the problem.
It may take some resources to do so.

I suggest doing a compression test. On 2 stroke engines with a symptom of a rattle in the engine, it is usually excessive piston to wall clearance, also known as piston slap. If your compression is low, around 100 psi or less, you should tear down the top end and measure the piston and cylinder for both sizing and clearance.

have a real mechanic check the timing chain guides, you may even need a new one, sometimes they stretch.

Have your egr valvle checked, if not operating properly it can cause engine 'pinging' which sounds like what u are describing. Let me know how it goes. countrycurt0

I had the same problem! I crawled underneath the car and discovered that a heat shield on the exhaust header pipe was corroded and rattling against the exhaust pipe. (Before the muffler)
I removed the portion and clamps and solved the problem. Give it a try.