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Cavitation: why your pool pump sounds like gravel

Updated : November 10, 2026 · Piscines VP

A sound like gravel or marbles rolling in the pump is often cavitation: the pump pulls less water than it needs and tiny bubbles collapse in the impeller. First check the water level, the skimmer and pump baskets, the pump lid and the suction valves.

If your pump makes a gravel, marbles or crackling sound, and the hand test changes nothing, the cause is often cavitation.

What’s happening

The pump asks for more water than it can get. Pressure drops inside the impeller, small bubbles form and then collapse. Those collapses make the gravel sound.

Checks you can do yourself

Turn the pump off before opening anything.

1. Water level: it should reach the middle of the skimmer opening. Too low, and the pump sucks air.
2. Baskets: empty the skimmer basket and the pump strainer basket.
3. Pump lid: tight, with a clean, lubricated O-ring. Bubbles in the strainer = air leak.
4. Valves: suction valves (skimmer, main drain) must be open.
5. Filter: a very dirty filter also makes the pump strain. Backwash if the pressure is high.

If the noise continues

• The pump may be too powerful for the plumbing. With a variable-speed pump, lower the speed.
• There may be an air leak on a suction fitting.
• A pipe may be blocked (leaves, a toy, ice early in the season).

Have the pump checked if the noise stays: cavitation wears the impeller and shaft seal.

Cavitation or vibration?

Cavitation is a sound inside the pump. Vibration is a drone carried into the ground that drops when you put your hand on the motor. Both can happen at once. See Noisy pool pump.

Not sure of the cause? Take the 2-question diagnosis →

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