I have a 2000 a6 2.7 t,I purchased a couple weeks ago. I hear a vacuum leak when driving .I don't hear it if the car is parked. My tranny is acting up I am assuming it is caused by the vacuum leak.. I was hoping someone could confirm that as well as tell me how to find and fix it.

 

check rubber boot near throttle inlet by diverter valves. Common problem is the center seam of the boot rips & leaks vacuum.

 

It could be a lot of places, so you can inspect it all or go to a shop for a smoke test. That'll definitively show you any vacuum leak to the atmosphere.