Sounds of Aliens From Space

Everyone hears that weird grinding, barking, alien dog noise right before an A320 takes off… and everyone thinks it’s the tail adjusting. But nope, that sound isn’t coming from the stabilizer at all. It’s coming from deep inside the landing gear bay, where the PTU (“Power Transfer Unit”) is basically screaming its way through balancing hydraulic pressure between two independent systems. It’s loud, it’s rhythmic, and it sounds like a dog trying to escape the walls, but it’s actually one of the mo