Engine noise in 383

I have this noise that just started. It's a high pitched clicking noise like I haven't heard before at idle. It's coming out of the driver's side valve cover breather. If you cover up the breather with your hands you don't hear it. It starts after the engine starts to warm up. Cold the noise isn't there. I've listen to the valve cover, block, exhaust manifold and intake with long screw driver on my ear don't hear it. When you increase the rpms above idle it's gone. Wondering if it could be a lifter. If so how would I prove it.

Kind of a clinking sound instead of a clicking sound. Have a recording but didn't see a way to post it.