Sloshing sound when starting cold engine, when stopping, when turning. Any ideas?
There’s air in the cooling system. The noise is from the air/coolant sloshing inside the heater core.
To purge the cooling system of air, get the engine up to operating temperature. With the engine idling, slightly loosen the upper radiator hose clamp. Slip a flat blade screwdriver between the hose and the neck on the radiator until all that comes out is coolant. Refill the cooling system as required.
Tester
If there is air in the cooling system, you can also purge the air by parking on a hill with the front end facing up the hill and opening the radiator cap while operating the engine. The air will rise because the radiator cap opening is now the highest point in the system.