I turned the engine on. Then heard a flowing river under the back seats, towards the middle. It sounds like when you are pouring water out of a bottle, or when a small stream is moving through rocks. I turned the engine off and the sound went off ten seconds after. Thought it could be the coolant, but can't figure out why does it sound from under the back seat
Sounds like the fuel pump/fuel through lines to me. Do you get the sound when you turn your key to the engine on position without going to the next click to actually start the motor?