Hiya car geeks,
I have 2005 Nissan Altima which I bought when nissan did an overall makeover. It has 102k miles on it. Offlate I am observing that when the car is shifting gears (automatic), I hear kind of some fluid moving through near the front passenger seat. I looked under the seat and the searched the whole car to see if there is a half empty water bottle thats making the sound. I dont see it though. Am I looking at some problem?
You might have the A/C evaporator drain hose checked for a clog as the evaporator is located underneath the dash on the passenger side. This can allow water to build up in the evaporator case and if that is the case it should be a very easy fix.
Also, check the drain holes in the right front door. I’ve had this happen to me. It is an easy problem to solve. Look at the bottom of the door and take a stiff wire and push it up the hole.
I hope it is what those above have suggested. A similar sound happened to me when my head gasket was going bad. The exhaust gases were being circulated through the cooling system.
I have higher hopes and want some air in the cooling system to be what is causing the noise. I want it to be a non-issue. So when the engine is fully warmed up, I would try parking on a hill with the engine running and letting the air go uphill to the radiator.
It doesn’t work often enough to really be recommended. It seemed to work for me once or twice on my 70s cars and trucks when I had lots of air in a system after changing anti-freeze. It was long ago and far away. As Bob Welch chants “If it seems like a dream, it’s got you hypnotized”. I listen to old Fleetwood Mac sometimes whenever it’s a Mystery To Me.