In every fuel injected car that i drove that had electric fuel pump, i always hear the fuel pump buzzing sound after turning the ignition on however after a couple of seconds the buzzing sound goes away. Why is that? Is it because after a couple of seconds the pump fully pressurizes the fuel and this causes the buzzing sound of the pump to be "eaten away" so we dont hear the sound anymore?
Most fuel systems have a pressure-switch. So when the power is first applied the fuel system is unpressurized. The fuel pump is then turned on to build up pressure so the engine can start.
Once the fuel system reaches the designed pressure the pump is turned off.
If you listen closely you will hear the pump reactivate from time to time as the engine is running to keep the pressure up.