Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 14000
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Issued New Clearance; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Aircraft
Takeoff was uneventful as First Officer was pilot flying. Passing 10;000 feet; de-sterilized FA's (Flight Attendants); turned off lights as we continued climb. Switched from [Departure] freq to Center. Upon check in with Center; appx 12-15000 ft; I noticed a medium burning electrical smell; didn't mention anything at first to see if smell would dissipate; it didn't. Appx 3-5 mins later; passing FL180 in climb felt a continuous strong vibration under my floorboard followed by a loud 'Thud' which sounded like a metal door hitting a door frame. It was at this point that the burning smell got worse. I told the FO (First Officer); he has the [aircraft] while I called the #1 FA. I asked him if he heard or smelled anything. He did in fact confirm the strong vibration coming from under first class galley. He did not smell anything but the #4 FA in back of plane said she smelled a light burning odor. It was at this point that I realized something was going on. I told FO we're going to turn back to [the departure airport]. I told [Center]; we need to head back for a mechanical problem. I then called #1 FA back and told him we are returning; no evacuation; planned and will be on the ground in 15 mins; he had no questions and I told him to start getting cabin ready for landing.Upon landing; and talking with our local company maintenance; he concluded quickly that one of our blower fans for extraction valve for avionics cooling had malfunctioned.
A321 Captain reported returning to departure airport after experiencing vibrations and a burning smell.