THANKS EVERYONE FOR THE SUGGESTIONS!
Ok, so I disconnected the city water, opened some faucets to drain / relieve pressure. Cleaned out the pump filter screen (it wasn't dirty at all, just a few grains...) then turned on the pump and ran some water.
Side issue/ other issue: Don't know what causes the pump to make a loud clattering/hammering noise, but I remember this happened once before and if I remember correctly, I just opened the fill port cap and it went away (?) So this time I opened the water tank drain and let out about a gallon of water. Now the pump has returned to quiet operation. Perhaps when the tank is overfilled, some vaccum created? not enough air in the tank? I dunno...
Anyway... I have now turned off the pump and turned the city water back on and now I wait to see if the tank overflows again..
Thanks for your help everyone. I will reply back if this works or not.
Even if this works, I think I will add an outboard check valve because it sounds others have had this same problem.
