What causes the sound of water entering the engine?

[DelAlice]

If the coolant is insufficient or the radiator is clogged, it can create a cavity inside the heater core. When coolant flows through this area and impacts the radiator walls, it produces a water-flowing sound. A bubbling sound, similar to blowing air through a straw submerged in water: For the power steering pump, this sound is commonly associated with the expansion tank or the mechanical hydraulic power steering pump. There are two typical scenarios where the hydraulic power steering pump makes this noise: one is a power steering fluid leak, which is common in older vehicles over time. When the fluid level drops and air gets mixed in, this sound occurs. In such cases, topping up the power steering fluid usually resolves the issue. The sound of flowing water: This sound is often heard from the heater core. It’s rare for the engine’s internal coolant passages to produce such a noise because, first, the engine’s operational noise typically drowns out the sound of flowing water, making it difficult to hear from the driver’s seat. Second, the engine’s internal cooling system is usually free of air, with coolant flowing tightly along the cooling system pipes without any water impact, so it’s unlikely to generate a water-flowing sound.