03 a4 1.8t vaccum problems... maybe a valve?

Got an 03 A4 1.8t. Lightly chipped and no other modifications.

Heres the issue. Under acceleration I can hear a hiss from the engine
compartment. No noticeable change in performance but sometimes when I
come to an idle, its rough and I can hear a little hiss. I get out..
pop the hood and identify the source of the his... and give it a
thump. The valve snaps itself together, the hiss goes away and the
idle returns to normal. What valve is this? Does it normally snap
apart like its doing? If I removed it from its assembly I believe it
would just fall apart. Is that normal?

http://jake.rakestraw.com/images/engine.jpg
This is a shot of the engine compartment with the questionable valves
location circled.

http://jake.rakestraw.com/images/valve.jpg
This is the actual valve. You can see the dust free fingerpriunt on
the side when Ive been pushing on it to pop it back into place.

Any ideas?

Jake