Passenger freaks out over noise plane is making as they're about to board flight but there's a perfectly normal explanation

A mysterious engine noise heard by a passenger about to board a KLM flight recently sparked curiosity online, but plane experts say it’s perfectly normal.

A traveler recorded a short video of the sound and posted it on Reddit, asking fellow users to explain what was happening inside the jet engine.

The rattling or clattering was unusual enough to raise questions from non-experts, but those in the know quickly chimed in.

As it turns out, the phenomenon, also known as windmilling, is common and completely safe.

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The fan blades are deliberately loose, but it’s totally safe

When an airplane is parked or taxiing, wind can blow through the engine, causing the fan blades at the front to rotate freely.

This process, called windmilling, often produces a chattering sound as the blades shift slightly within their mounts.

According to aerospace engineers, each blade is attached to the central hub with a dovetail joint that is deliberately designed with some looseness.

At low speeds and in cold conditions, these blades may rattle, but once the engine starts, heats up, and spins at full power, centrifugal force locks them firmly into place.

One expert explained on Reddit:

“The fan blades clatter around a bit when the wind spins them, but they can’t escape. The engine is continuously monitored for abnormal vibration, so there’s nothing unsafe about it.”

Another user added that manufacturers intentionally design the system this way to accommodate thermal expansion and ensure long-term reliability.

Plane engine noises can be very unsettling for passengers

The video sparked plenty of lighthearted comments alongside the technical explanations.

One user joked that the sound was ‘the handful of coins the passenger ahead of you threw in for luck’, probably referencing the time an elderly Chinese passenger threw coins into a plane engine a few years ago.

“It’s about to spit out tonight’s winning lotto numbers,” quipped another

A third commenter claimed the noise came from ‘the hamster that drives the turbine trying to escape again’, which is probably related to the hamster that was briefly a truck driver.

Despite the humor, the situation highlights a common issue in aviation: an unfamiliar engine noise can cause understandable concern for passengers.

After all, nobody wants to be on a plane with any potential mechanical issues.

Modern jet engines are incredibly complex, but they are also designed with multiple safeguards and are inspected regularly.

Of course, even a modern plane engine is sometimes no match for a simple bird, as the impact of a bird strike can be absolutely devastating on an airplane.

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