My car has developed a loud metallic tick noise that happens every 30 seconds or so at idle. I would guess it might be the vacuum pump or belt tensioner? The car runs completely fine otherwise and the idle is smooth even with the tick noise present. I can't pin point where the noise is coming from so before I start taking things apart I figured i'd see if anyone has encountered this before.

IMG_3738 by jon allie, on Flickr

IMG_3739 by jon allie, on Flickr