Air carrier pilot reported a loud noise while at the gate and during taxi; the noise continued along with an odor throughout the cabin. The crew returned to the gate for maintenance.

Narrative

On Date; the flight [was] from ZZZ to ZZZ1. Once we decided to push back; we started Engine 1 and on completing the push back; we started our Engine 2. After the engine start; we moved to our normal procedure which is to transfer the packs to the engine bleeds and shutdown the APU. As we did; we immediately began to hear an extremely loud noise followed by a very strong smell. The noise was overwhelming; I could barely communicate with the First Officer; I could not hear my radio and neither could my First Officer. I could not communicate with my Flight Attendant. We decided to change the packs and bleeds configuration multiple ways but the noise and smell were only getting worse so we decided to return to the gate. As we returned to the gate we messaged Dispatch; however; we did not receive any reply. We proceeded to perform our normal shutdown checklist and the noise only went away once the avionics master switches were off. Once we were able to resolve the issue we immediately called Dispatch to report the situation. The Flight Attendant and the passengers were also able to hear the noise and observed the strong smell. Maintenance came and resolved the issue. After that we were able to resume our flight; no further issues noted.A lack of communication caused by a maintenance issue that brought an overwhelming loud noise followed by a strong smell requiring an immediate action. I took the steps necessary to make sure the passengers were safe and get the issue quickly resolved.