You stated you had valve covers off - notice any rocker arm markings on covers?
Did noise get louder?
Could it be pushrod-to-guide plate clearance?

 

I have checked all of the above mentioned but haven't found anything. The noise has been there almost 5k miles now and not any better or worse. My mechanic had the valve covers off and didn't see anything obvious. I could have sworn it sounded like an oil starved rocker. It still runs every bit as good as when I bought it 5 years ago. Mechanic told me he heard a similar noise in a Ford Triton engine that went away after 3 oil changes with Sea Foam added. I have had it go completely away for a day or two after I run it pretty hard.

 

so you have run it without the belt and it still makes the noise?

 

I had another 94 camaro z28 6 speed in the early 2000's and it developed a chirp or whistling sound but it was coming from the exhaust manifold. It would do it when the engine was above idle. I figured it was the catalytic converter so I pulled the exhaust loose from the back of the cat and it was obvious it was clogged. Living out in the country at the time, I just beat the comb out of it. I put everything back together and drove it and I could not believe how much faster it was. It had slowly clogged and the power loss was so gradual that I had thought I had just gotten used to the power of the car so I was surprised at just how much power it had lost. It was probably a 50 hp loss over time.

 

Old post, but I have the answer. It was the water pump. The noise started about 8k miles after I had a shop change the leaking water pump. The replacement NAPA pump started leaking out the weep hole about a month ago. The chirp got quieter. Had a new water pump (not NAPA) installed, and the noise is gone.

 

thank you, not many come back and let us know once they find the issue. have a great independence day.

 

i remember that noice more like a squeak from the water pump was clear though what it. was weep hole