What causes the sound of water sloshing when driving?

[Autumn]

Possible causes include low levels of fuel in the tank, insufficient coolant or windshield washer fluid, air trapped in the heater core requiring bleeding, or a faulty heater valve. Below are relevant details: 1. Low fluid levels: If the fuel tank, coolant, or windshield washer fluid is low, try refilling these fluids first to troubleshoot. If the sound comes from the front of the car, refill the coolant and windshield washer fluid; if it comes from the rear, refill the fuel tank. 2. Water accumulation: Water may accumulate in the doors, especially if small advertisements or cards are frequently inserted into them. When water enters the door, these materials can turn into paper sludge and clog the door's drainage holes. Water may also accumulate in the side rails if their drainage ports are blocked or if the protective stickers on the drainage ports were never removed.