I don't know how long this has been going on because I normally drive with the music on and windows up. But this weekend it was warm enough to have the windows down. I noticed at a stop that there was a hissing sound that was sometimes intermittent and other times a steady hiss. I believe it only does it at idle and goes away as soon as I shut the car off. I looked under the hood and it sounds like its coming from the drivers side near the intake manifold towards the back. I felt around and wiggled some hoses but didn't feel anything or hear anything change. I didn't want to do too much more and risk burning myself on something. Any ideas?

I don't know if this is related and I'm not sure how long it's been going on but I noticed a strange vibration while stopped in the shifter. Seems to go away after I start moving. It might have been going on for a while and I just dismissed it as being normal because I get some slight vibration pretty much any other time, usually it's not noticeable except when I'm on a long drive at 65MPH. How much vibration should I be feeling?

Forgot to mention: 2001, 1.8T, Quattro, manual, 45k miles, plugs, all filters except fuel, and oil changed within 2,000 miles.