After a major service of my Honda MRV car 2005 model, I started hearing sound of liquid movement while driving. Honda service center identified the sound coming from the fuel tank. They had no solution to the problem and said it does not effect car performance. It is annoying to keep hearing the sound especially when breaking or moving on uneven road.
Seems the design of the baffles in the fuel tank cause a noise, but in my limited search, owners noticed this when the cars were purchased new. If the sound varies with the amount of fuel, that is probably your problem.