If a pump sounds like it's pumping rocks, what is the most likely cause?

When a pump sounds like it's pumping rocks, the most likely cause is cavitation. Cavitation occurs when there is a drop in pressure in the pump that causes the liquid to vaporize and form bubbles. These bubbles can collapse violently as they travel to a higher pressure area within the pump, producing a knocking or grinding noise that resembles the sound of rocks being pumped. Not only does cavitation create this characteristic noise, but it can also cause significant damage to the pump impellers and other components over time due to the shock waves generated by the collapsing bubbles.

Understanding cavitation is crucial for maintaining the pump's efficiency and longevity, as recognizing the symptoms early can lead to prompt corrective measures, such as ensuring adequate suction pressure or reducing the pumping speed. The other options, while they may exhibit distinct issues or sounds, do not typically produce the rock-like noise that is indicative of cavitation.