Today, my transfer pump was making a clicking sound from startup to shutdown.  It seemed as though it was pumping into the header tank just fine though as fuel was passing back down through the overflow tube from header back to main.  The sound was similar to when the pump starts to run dry but maybe a bit louder.  Is this a sign that pump could be failing?  I had about 12 gallons in the main tank so it was nowhere near running dry?