DIAGNOSIS Air is trapped in the water intake tube or the pump is cavitating due to a partial blockage.
FIX This is often a priming issue. Ensure the water reservoir is correctly seated and full. With the reservoir removed, check the small black rubber flapper valve at the bottom. Ensure it moves freely and isn't stuck. Re-seat the reservoir firmly. Run a water-only brew cycle without coffee to clear any air.
IF THAT DIDN'T WORK Mineral scale or coffee grounds may be blocking the internal water inlet. Disassemble the reservoir assembly to clean the inlet screen and the tube that connects to the pump.
HEADS UP Always use the 1-4 cup setting when brewing small amounts. Using the standard setting for less than 5 cups can cause overheating and pump noise.