Boeing 757 flap screeching sound (?)
Hello, What causes this very distinct screeching sound inside the Boeing 757 cabin, which can be heard when the flaps are operated? I used to think it was the ADP "screaming" under the belly of the airplane, but I just noticed that the 757 doesn't have an ADP (by watching pictures of the 757 overhead panel). Seems to me that there are only engine driven pumps and electric pumps, correct? Do they cause the sound? Thanks in advance