I must keep the pump to our Petmate fountain clean to keep it quiet. Pull the pump out of the fountain and check it for scummy buildup. Buildup will make it suck too hard and therefore too loud.

Depending on the quality of our current water supply, this happens more frequently sometimes. I think some people do not experience this build up problem because their water supply is better.

I have started using bottled water and it seems to help. It's also worse in the summertime. Since you live in the southwest, you may encounter this build up more frequently.

PM me if you want details about how I clean the pump.