Strange noise at low alititude

[JohnnyRocket]

Might seem like an odd question... but travelling on the A321 and A330, after the flaps have been retracted, I have often heard another noise - medium to high pitched... almost like you might hear as if someone were putting on the breaks on a car on the ground.

The noise is usually apparently at low altitude particularly one to two minutes after takeoff... it is also apparently on desecent and can be heard if it's quite windy and the aircraft is trying to correct itself.

Thanks,

[chiglet]

Gear [Undercarriage/Wheels] being Retracted/Extended.....
watpiktch

[Juliet Sierra Papa]

Gear [Undercarriage/Wheels] being Retracted/Extended.....
watpiktch

Not 1 or 2 mins after t/o, this would have been done along time back

Maybe final few degrees flap retraction which may not be obvious from viewpoint but surely not so early into climb?

[JohnnyRocket]

I thought originally that it might be the final few inches of flap retraction but actually this noise continues after the flaps are at 0.

I would liken it to the sound you might get from squeaky brakes on a bus... know what i mean? Very light but still noticeable.

Also, I noticed it on landing in very windy conditions. Each time the plane was being buffet one direction or the other, each time we were being put back on course, the noise came with each gust of wind.

[Bus429]

If it sounds like a dog barking, it could be the hydraulic power transfer unit (PTU).