The submitted content does not constitute an aviation news article and cannot support a meaningful analytical summary. What has been provided is a brief Reddit post consisting of a single sentence and a link to a Reddit-hosted video — a video that is inaccessible to this system and contains no transcribed content, no identified aircraft, no location, no operational context, and no verified facts of any kind.
Without knowing the aircraft type, the phase of flight, the power setting, the configuration, or any other observable detail, it is not possible to responsibly identify or explain the sound source. Aircraft produce distinctive noises for many reasons — hydraulic pumps, thrust reversers, leading-edge slats, auxiliary power units, turbofan fan blade pass frequencies, prop resonance, landing gear doors, and dozens of other mechanical and aerodynamic phenomena — but attributing any of these to an unidentified video requires actual data.
To receive a professional-grade analysis suitable for working pilots and aviation operators, please provide a sourced news article, an NTSB report, an FAA advisory circular, an accident brief, an airworthiness directive, or similar verifiable aviation content. That kind of material can be analyzed in depth.