Hi, I have a '99 Z24 and I've changed the timing kit 3 times in 6 months.
Over 3.000 rpm it starts to sound like the chain hitting the metal. I have no problem with power or timing, but the metallic sound is not normal.
When I change the timing kit, it works fine for a month, but later the sound comes back.
Somebody told me to change the chain tensioner for a '96 one. I did, but the same.

Anyone has an idea to help me?

What tensioner do you have? make sure when timing that the 8mm bolts go through the cam spocket into the block and the point on the crank is marked up with the block.

I also have the same problem but it just started at 147,000 miles. I have a 97 chassis with a 99 engine. above 3,000 rpm it clatters. I haven't torn it apart yet cuz i only drive it a few miles a week but im going to need to fix it after the holidays. What tensioner should i put in it? the stock one for the 99 engine from GM or a different one? and should i also change the chain or anything else when im in there replacing the tensioner.

Now I have the '96 tensioner on the 99 engine. Today it's worst, it started to sound just like a blender... low or high rpm it's the same....
Corey, you should change the following:
- Chain tensioner
- Chain
- 3 Chain guides (Upper, left and right)
- Camshaft sprocket
- Crankshaft sprocket

well carlos why didn't you use the 99 stock tensioner and why would i need to change the camshaft sprockets? do they wear or why?
and wouldn't you change the water pump as long as you have that all apart?

Last time I changed the timing kit, somebody recommend me to use the 96 tensioner, so I did. Previously I used the 99 one but the same noise after a month.
Well, about the sprockets, I purchased a "Timing kit" which included both crankshaft and camshaft sprockets. I've never heard about a broken sprocket, but theoretically they wear after time, so there is no harm replacing them.

About the water pump. Honestly I did not changed it because, in order to change it you have to disassemble the exhaust manifold. You can change the timing components without major disassemble. My water pump has 144.000KM (Km, not miles) with no problems...

However, I'm going to change it very soon because a crankshaft bearing started to sound today, so I stopped my Z24 and started to prepare it to rebuild the engine....

a haynes manual would help you alot!