love the new car, but having a problem with weird gas noises

[karotZ]

Is it like a hissing sound? I know you said farting sound, but if its like hissing,
does the car have stock exhaust? Are the cat converters stock?

And just to clarify another thing, you said chug-a-lug, do you mean you hear
a chattering sound like 2 small metal pieces clashing when on idle? If the
chattering chug-a-lug sound is separate matter from the farting noise, then
what you are hearing is an early release of the clutch. We have the noises
clutch of all cars.

If none apply, get a 2nd opinion from another dealership. Do not mention to
the other dealership that you had this inspected, see what they say.
If the 2nd opinion ties to the first theory, then you as a certified pre-owned
buyer should not be dealing with this. Nissan needs to flush the system to
get rid of that build up. That build up sounds like you're about to get bad
mpg.