So I have noticed this for a good while now... but on occasion when I start my car, a noise that almost sounds like a toilet flushing comes from the rear of my Audi. I saw that a couple of people mentioned this sound, but haven't seen anyone post what it could be from. Looking for some insight!

 

you stalking about the fluid noises that happen right after it starts? i think its gas being returned to the tank. If you remove the rear seats you can hear it much clearer

 

Oh, ok. So its not a bad sound then, is that correct?

 

I posted about this same thing somewhat recently. The answer I got was that it is the central locking pump (CLP) operating. I was informed that this is not a bad sound and nothing to worry about, as other members said that they have had this sound for years with no negative effects. I'm just going with that for now, but let us know if something explodes one day!

 

central locking pump moves air ao i doubt you would hear a liquid sound ? the fuel tank however does move liquid and thats what this toilet noise could be

 

I was always told it was the central locking pump as well, but the fuel tank seems like a far more plausible explanation to me

 

lol ok. Well that works for me, I just wont worry about it.

 

lower the back seats and remove the black sheet metal cover to access the tank, the noise is way more audible.

 

On Quattro A4s, the gas tank is U shaped to accommodate the driveshaft. My understanding is that there is a 2nd pump within the fuel tank which moves fuel from one side of the tank to the side with the actual fuel pump in it. Thats the noise you are hearing when starting up the car.

 

Thanks for the info