RichieC wrote:
Before you go whacking the pump with anything. . .
Remove the pump.
The pump, from the factory, has push-on electrical connectors.
Sometimes the electrical connector's metal degrades over time, either from micro arcing or dissimilar metals.
Inspect the pump push-on electrical connectors - both sides, female and male terminals.
If you see any blackened areas on the connectors you will have found the problem.
This is exactly the problem I had with mine, where the water pump plugged into the motorhome wiring harness. Didn't have to remove the pump to work on the connector.