Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition
Aircraft
In cruise at FL340 a loud sound of air started coming from behind the flight deck door. It was an abnormally loud sound and followed promptly by a call from the forward flight attendant. The flight crew verified normal cabin pressurization and door indications and the Captain (pilot monitoring) answered the call. The forward flight attendant determined the sound was from the forward galley area. The flight crew contacted ATC to receive a lower altitude in case a pressurization problem were to arise. [We requested priority handling] as the cause of the loud airflow was unknown and the intended airport of landing was ZZZ.During the descent there were no abnormal indications on any aircraft systems; the only indication was the loud noise. On the descent the flight crew had communicated with the flight attendants; passengers and sent the information to dispatch. At this time all aircraft indications remained normal; dispatch informed us an additional CRJ900 was available at ZZZ1; and our current weight showed over max landing weight for ZZZ. ZZZ1 was approximately 25 minutes from our current location and would allow us to burn fuel to land below max landing weight. As all systems remained normal; ZZZ1 seemed to be the best alternative. The aircraft landed at ZZZ1 and maintenance was called with write up. Flight was changed to the available aircraft and continued on to [original destination].Earlier in the day the forward cargo door had failed to shut (caution indication) initially by the ground crew; but was indicated closed and locked (green) after a second attempt. Not positive what caused the sound; but it could be an option. The passenger door seal was visually inspected upon landing; but nothing significant was found.
The First Officer of a CRJ-900 reported hearing a loud sound of air escaping from behind the flight deck door.