Date: 201912
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Icing; Turbulence
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Exterior Pax/Crew Door
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Crew departed normally; climbed to cruising altitude and leveled off. Approximately 6-7 minutes into cruise; a sudden humming noise was heard from an unknown location. It grew gradually into a loud whistling sound with vibration. Crew was unable to determine source of sound. Lead Flight Attendant called shortly after inquiring about the noise. Flight Attendant informed [the] crew noise was coming from L1 boarding door. Crew cross-checked status pages and pressurization. All indications were green and normal. No EICAS MSGs were presented and crew communication was established.Crew requested descent from ATC to lower altitude. Center assigned 10K ft. Captain called for the donning of cockpit oxygen masks. Crew assigned Pilot Flying to First Officer. Captain attempted to communicate with flight attendants to investigate noise. Sound was too loud for FA (Flight Attendant) to hear crew. Inquired ATC on nearest airport; ZZZ1; at 45 miles. Weather there was ¾ mile visibility and a ceiling of 900 broken. Crew determined that ZZZ was the nearest suitable airport and proceeded there. Requested and was given direct to the destination; ZZZ. Center provided priority handling for us. Crew notified Dispatcher of priority handling and intentions. Dispatcher concurred with decision. Crew removed O2 masks at 10K and proceeded to destination. No limitations were exceeded. No FAR's were violated. Crew requested CFR (Crash Fire Rescue) equipment to be standing by. Aircraft taxied off runway under own power and rescue vehicles were told to stand down.


Second narrative: Upon reaching FL220; crew accelerated aircraft and upon cruising at approximately 300 kts; a noticeable humming sound appeared. Sound got more prevalent with time. Proceeded to get a call from the FA1 (Flight Attendant) several seconds later asking us what was going on and if we heard the same noise. There were no erroneous EICAS indications and everything was operating as normal. The sound was loud enough for the FA1 to have difficulty communicating with crew. Likewise; cockpit crew had trouble communicating between each other due to the noise and vibrations. Crew evaluated the situation and requested a lower altitude from ATC. ATC granted 10;000 feet [and] no further assistance was required at this time. Crew continued to troubleshoot the issue as they donned the oxygen masks.Crew then requested direct destination and upon receiving that; were informed that Center had [provided priority handling] for us. Crew notified Dispatch and proceeded direct to destination airport after evaluating ZZZ1 as an alternate. Crew proceeded to ZZZ due to low ceilings and viability at surrounding immediate airports; smaller airports with shorter runways and no ATC services in use at the time.Aircraft cruised to ZZZ at 10;000 feet and shot the ILS XXL approach. Crash; fire; and rescue were rolled out as a precaution. Aircraft landed safely and taxied to the gate where they were met by operations personnel and maintenance. No FAR's violated or aircraft limitations exceeded.


Synopsis: EMB-175 flight crew reported loud noise at the L1 door; requiring a diversion and a precautionary landing.