Strange noise

When you are on a plane and while you push back from the gate there is a loud squeaking sound. It kinda sounds like you are putting rivets on a car. Anyone know what that sound is?

im no expert but that could be the tires your hearing

I think it’s the hydraulic system getting all ready for the flight. Or is it the push back tug?

Are you talking ab out Airbus aircraft? Because I know what you are talking about but have only ever heard it on airbus aircraft.

If your talking about airbus, it’s the hydrolics getting ready. It sounds like a rivet gun.


Yeah, it’s like rubber tyres squeaking into place

It happens on the A320, It´s called the PTU (Power Transfer Unit).


Yeah that’s it. It sounds like a dog barking!

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The only squeaking-ish sound I hear is the flaps.

May not be familiar with this one because I haven’t been on aircraft for more than a year.


Listen to this. Skip to 1:20 for the sounds. The video description says what is happening.

It sounds very weird closeup!

And totally different on a Q400



Oh yeah! Now I remember!

It’s a very weird sound for what is related to the engines!

It may be the Hydraulics as other people said. Which may be why they test the spoilers and rudder when still at the gate.

“In case you’re wondering, the Power Transfer Unit (PTU) is designed to ensure adequate hydraulic pressures during single-engine operations. To conserve fuel, it’s fairly routine for two-engine planes to taxi with an engine shut down. Each engine normally pressurizes its own hydraulic system, but with a motor not running, that leaves one system without a power source. That’s where the PTU comes in, helping left power the right, or right power the left. Since it is activated only when the pressure falls below a certain level, the PTU cycles on and off, on and off, on and off. Due to pressure fluctuations, the noise will sometimes continue even after both engines are up and running. It also does a self-test when the starboard engine is started, so you’ll hear it then as well. Some Boeing aircraft also employ a PTU, but the operation is slightly different and it doesn’t bark like a dog.”

Airbus obviously likes dogs!


Pilots retract flaps after push so it might be the flaps retracting.

I think they would be setting the flaps rather than retracting them after pushback.


It happens after the pushback is completed! It’s just the engines starting up. Happened to me 2 weeks ago, it’s normal. I went on a 777-300ER from Manchester to Islamabad.

The flaps also make a noise but not that loud

When you start up and the hydraulic system pressurizes they will retract. If left shut down everything droops.

If that happens at all, it happens on stand not after pushback.