So after my car sits for a day or so, or sometimes just on a cold start, it sounds like somebody just flushed a toilet in my trunk (sounds like a whooshing of water through pipes) for about 5-10 seconds. after that it's just gone.
completely clueless on what this could be.

any ideas? :s

 

I get it too, water in muffer

 

Maybe the vacuum booster in the trunk (passenger side, back corner, under the carpet and storage bin). It's the module that powers the locks and such and it may have a leak in a line or fitting.

Not sure man but that's the only thing I can think of...

 

Water in muffler - I can see that too.

 

how would i get that much water in my muffler, to make it sound like 40 gallons of water just went through 3 inch PVC pipe lol. and i've never noticed any water in the driveway?

 

double post

 

its been winter here in minnesota for the past 6 months it seems like lol.
so wouldn't water freeze in the muffler after sitting all night and on a cold start?

 

Im down hear in Miami and i have the same sound when i cold start every morning.But i never see any water at all also.

 

I used to hear a similar noise in my 97. Turned out to be the central locking vacuum pump. I dunno if that one was just on its way out or what? Haven't heard that noise yet in the avant.

 

I remember reading that because of the rear driveshaft on Quattro A4s, the gas tank is U shaped. There is a pump that moves fuel from one side to the other where the actual fuel pickup is.

I hear it on my car too.