I believe that your thinking is close, but not quite right. That's assuming that you have the fuel system put back together. There would be a blockage when the whole system's together. You won't be able to push fuel through your injector pump. That would be your blockage That would also make the electric pump make more noise. When you press the Schrader valve on the filter head, you're releasing some of the pressure so the electric pump gets quieter until the pressure is built back up which should only take a few seconds.