Where on the car were you recording that from? Do you mean the kind of farting sound for lack of a better description? If you do, It sounds like a leak where the headers meet the pipes to the first set of converters. Mine sounded exactly like that when it was leaking. I still have a leak at my Magnaflow converter that kinda sounds like that too. Why it wouldn't do it in motion though I have no idea.
It could also be in your transmission.
The whole reason I went to 4.44's was because my torque converter started making noises in Park and Neutral. It was kinda of a whirring or humming sound though that you could hear it wind down when you shut the car off. Just some ideas from what I can figure out from the description and sound clip. Good luck man.