Ok I heard this a few times so far, and I thought it may have been water in my exhaust, so I left the car running to maybe evaporate the water sitting in there. Well, I thought that worked because I didn't hear any of that sound again for a few days.
Then I started my car one morning and I heard the sound again. I figured it was coming from the gas tank this time. I did bring my car to Audi a few days before to diagnose my clutch problem ($45 for telling me what I already knew, that the clutch was gone) and I mentioned the sound, but they didn't seem to hear it. Anyone have an idea of what it may be? It doesn't happen often, seems like only in the morning, or when my has been sitting in the cold for a couple hours. Thanks in advance.

 

fuel pump