Hiss from engine

[rhyek]

So I took my 2007 2.0 s to the shop today because I wanted to see what was causing a constant hissing noise I'm hearing near the engine. It's only noticeable if I put my ear very close to it, but the noise is there.
Thinking it might be a vacuum leak I had the shop test for that using a smoke machine, but they claim they didn't find any leaks and that the noise is actually coming from the PCV valve AND IS NORMAL.
Now, I haven't had a chance to go see the car yet, but I've no idea where this valve is, and most importantly if it can actually cause that noise I hear.
Any ideas?