Just to point out the obvious, pcv valves are one way valves by design. That's what is rattling inside them. No idea if the newer ones have the valve in them, but the pre-fuel injection PCV valves do. Same for the brake booster valve where vacuum line connects. It also is a one way valve.

 

That rattle is not a perfect seal.
I have pulled several brand new Pcv off the shelf at the parts store.
Could blow air either way. That's why we recommend check valves in the Pcv line.