weird sound during driving

When the Prius is READY and the gear selector is in P, depress the brake pedal repeatedly. You will hear the brake actuator pump run periodically. This is a normal sound. That pump is required because Prius does not have an engine vacuum-operated brake booster assembly.

If this is the same sound as the one that you are asking about, then you do not need to worry.

Also, the Prius will make various other sounds that a "normal" car may not make. For example, the air conditioning compressor has an electric motor which makes a distinctive sound when the compressor is running. The inverter makes a high-pitched sound when the Prius is READY. 4-5 hours after the car has been made IG-OFF, a pump will run back in the fuel tank area, checking the integrity of the fuel tank and lines.

North American cars have a coolant heat recovery system pump that runs for several seconds upon start-up and shut-down, to circulate hot engine coolant and speed up engine warmup for emissions control reasons.

If you do not see any warning lights on the dashboard, you probably do not need to be concerned.