Okay, so I’ve been hearing this strange sloshing noise in my Jeep Liberty 2005. It happens when I start off from a stop and usually around 15mph. It seems to be coming from the front of the vehicle (engine). And I’m not the only one that has heard it so I’m not crazy 
Any ideas?
Low coolant level could cause this as an air pocket forms in the system. Usually it is the heater core making this noise as water is moving around. Our Dodge Magnum would do this very near the 30K mile mark. I had the fluid “serviced” and it went away. Fluid service is just draining and refilling I think but either way it was gone.
Alternately, it could be a drain back from the air conditioner plugged causing the condensation to build up and not be evacuated from the car. This would be noticeable by other signs like a foul odor present from the dash vents because mold would be starting to form.
Another possibility is plugged drains in the rocker panels or doors allowing water to be retained.
Besides the the other comments, it could also be a plugged AC core casing. It is supposed to have a hose so it can just drain under the car (that’s why you usually see a puddle of water under the car when it is sitting still after you’ve used the AC). The hose sometimes plugs up. Find where it normally drops and run a pipe cleaner through it.