After Y'all scared the BeeJeebees out of me on the PCV, I went out and checked mine. It didn't rattle but was clean as a whistle. It still works though because it's just a very simple check valve. I could only get air through in one direction.

If it makes you feel better to replace it if it don't rattle then by all means do so (they are cheap). I prefer to just keep mine clean and make sure it's working properly.

CAUTION: after cleaning it, dry it well before you start blowing into it. Brake cleaner tastes really bad and will burn your eyes pretty bad. (I'm being sarcastic - don't stick things into your mouth after taking them off of your car).