As a former dealership technician and field service engineer for GM I had to get to the bottom of this noise. Below is information I pulled from the Toyota Information System on the EVAP system operation. It's not the fuel pump, but the leak detection pump that is mounted right by the fuel tank. Bottom line - Normal.
1. Key-off monitor
This monitor checks for EVAP (evaporative emission) system leaks and canister pump module malfunctions. The monitor starts 5 hours* after the engine switch is turned off. At least 5 hours are required for the fuel to cool down to stabilize the EVAP pressure, thus making the EVAP system monitor more accurate.
The leak detection pump creates negative pressure (vacuum) in the EVAP system and the pressure is measured. Finally, the ECM monitors for leaks from the EVAP system, and malfunctions in both the canister pump module and purge VSV based on the EVAP pressure.
• The canister pump module performs a fuel evaporative emission leak check. This check is done approximately 5 hours after the engine is turned off. Sound may be heard coming from underneath the luggage compartment for several minutes. This does not indicate a malfunction. Pinpoint pressure test procedure is adopted by pressurizing the fresh air line that runs from the canister pump module to the air filler neck.