Is this normal? · On the ground
The cabin lights flickered or went quiet at the gate
Short answer
Normal. Power is switching from the auxiliary power unit (APU) or ground power to the engines.
Where this comes from
Thunks, whirs, chimes and the famous "barking dog" — what you're hearing, from gate to gate.
Read: Normal sounds on a flight
Based on: FAA Airplane Flying Handbook (FAA-H-8083-3); FAA, "Turbulence: Staying Safe" (seat belt sign rules).