What’s this sound?

Hello everyone. I was watching some trip reports and I came across a flight with a CRJ900. Everytime I watch a trip report on a CRJ, I always hear this beeping sound, typically most heard around takeoff and landing. I have never heard any sound like this on any other aircraft. I even heard it myself on my flights on an American CRJ a few weeks ago. I don’t know if it’s just an engine sound or the APU but if anyone can tell me what it is, that would be great. Skip to 46:17 to hear what I’m talking about. https://m.youtube.com/watch?v=PS0MfDJAu6M

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What sound are you talking about… I hear the engines running and the A/C and thats about it

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I messed up on the video time stamp. It’s actually 46:17. The sound in the background

I don’t hear anything

I messed up on the time stamp. Skip to 46:17 in the video. The subtle sound in the background.

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Just edit your post😁

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Even then I still hear engine sounds

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Its like a duck quacking? @Jack

I don’t think there would be a duck on a plane😂

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If that’s what you want to call it. I literally can’t describe the sound at all. But it’s there.

Hence the term "like"😉

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I mean the closest I can think of is the flaps extending🤔

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It’s like a very slow beeping sound. It’s clearly not the flaps since no flaps are being extended or retracted.

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My best guess since it’s over the wings and fuselage, its some type of hydraulic pump, similar to the dog barking noise on the A320. PTU I think?

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That makes sense. The sound is also a lot slower at cruising and then the sound speeds up during takeoff and landing.

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Flaps being extended?

That’s what I suggested, but no, it’s not.

ARe you sure? The flaps go down and that sound comes on?

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Well idk😂

Idk what video yall are watching, but at 46:17 the flaps are very clearly being lowered, which is what the sound is

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