While draining the air tank I removed the drain plug and with the compressor on, tilted the unit to facilitate drainage and to dry out the tank. Suddenly, the unit (I believe it was the pump, because the motor ran ok) began to screech, so I shut it off right away. I thought maybe by tipping the unit I had caused the oil in the unit to flow away from where it was needed, so I let it sit awhile to give the lubricant time to flow back to where it belonged but no luck. Even after a couple of days, the problem persists. Porter Cable Customer Service suggested it might be the bearing. Anybody out there able to help me with a diagnosis?