My 95 f150 has a vacuum leak somewhere near the drivers side (I think). I can hear it when I shut my truck off. Also when I am in a low gear or somewhere around 40-50 mph there is a vibration that only occurs every once in a while. Now I have got a tune up and a new carrier barring (other one was shot) and I have checked my U-joints and I have not been able to find the source of my problem, so I have a couple of questions...

1. What is the best way to check for a vacuum leak?

2. Is anyone else having this problem? If so what did you do to fix it?

3. Is this something small that I shouldn't worry about or could this be something more major?

4. Finally, could this vacuum leak be connected to my vibration?