Hi and welcome to Just Answer.I will try and assist you today with your question.Please don't click on accept unless you feel satisfied with my assistance here.
I have seen the bearings in some of the rocker arms on this engine come apart and can cause this as well as some of the lifters fail and cause this as well.
If you can isolate what side this noise is heard at most this will aid in locating the faulty or noisey component.
You would then most likely have to remove the valve cover on that side to then inspect and locate the failed component.
If you have had any coolant leaking into the intake which can be common from failed lower intake gaskets this can cause the lifters to develop this type of noise and can also cause bearing failure as coolant acts like sand paper on the bearings in this engine.
Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!