Let’s talk about the unusual sounds and feelings you might experience during a flight...That "pressed into the seat" feeling or the "stomach drop"
Whether you feel crushed into your seat during takeoff or like your "stomach is in your throat" during certain landing phases or turbulence, you are simply feeling the effects of G-forces. You aren't used to them because, in everyday life, you don't move at the speeds or follow the trajectories of an airplane. You can find more details in [this post].
"We just took off, but the engines suddenly lost power!"
Don't worry. To take off, a plane needs a massive amount of energy, and the engines are often used near their maximum limit. Once airborne, all that energy is no longer needed, so the power is reduced to a "climb thrust" setting. Check out the post on [this post].
Noises and vibrations from outside or under the floor
An airplane has many moving parts that are activated during different phases of flight. Many of these use electric or hydraulic motors that make various noises when operated. The most common sound you’ll hear is the actuator for the "flaps" and "slats"—surfaces used during takeoff and landing to increase wing efficiency at low speeds (see this post).
Another typical noise, sometimes accompanied by vibrations, is the speed brake (or spoilers). As the name suggests, it’s a device used to "brake" or slow down while in flight (usually during descent). To do this, panels open up into the airflow—a bit like opening a car door while driving on the highway!
Shortly before landing, you’ll hear a loud "thump" beneath your feet, followed by an increase in wind noise. This is the main landing gear leaving its housing under the "belly" of the plane, extending, and locking into the landing position.
A sudden roar of power right after touchdown
These are the "reversers." The engine power is increased, but this time the airflow is diverted forward to help slow the plane down on the runway (see this post).
Whistling or hissing near the doors
In flight, the cabin is pressurized to allow everyone to breathe normally. Occasionally, a door seal might not be perfectly airtight, allowing a tiny stream of air to escape and creating a whistling sound. This is not dangerous in any way—it’s just annoying!
DontWorryFlyHappy!