Magnetic buzzer causes interference in the circuit
Read the spec on the device - it has a terminal resistance of 17 Ω to 23 Ω. At 17 Ω and 5V you'll be drawing 294 mA yet the device is typically expected to run at 80 mA (max).

Put a resistor in series with it and read the data sheet. If you still have problems with your power supply after putting the resistor in series then it's your power supply more than likely.