Troubleshooting 12 volt pump

sundug

Hi,

  I have an older Hartell 12 volt circulator pump CP-3B-12HE. It's a part of my SHW system linked to below. It is directly driven by a 12 volt 10 watt PV panel. It recently started making a regular tapping sound synchronized with RPM, but only at slow speeds. It runs fine and sounds normal at higher speeds. I was hoping someone might be able to help me figure out if it's in the magnetic drive, a bearing or impeller problem. Thanks, Doug

http://www.builditsolar.com/Projects/WaterHeating/DougsSolarWater.htm