What causes noise when raising or lowering flaps on new planes?

Question

The newer planes like the 767 make a groaning, howling noise when the flaps are raised or lowered. Older planes (737, 747) don't seem to do that. I presume they have changed the technology to save weight. What is that new technology?

Answer 1

Well they raise the flaps to save from braking and using more fuel, so maybe the newer ones are more fuel efficient? And they are letting you know that they are working so no one freaks out when they don't hear those go up and down! :)

Answer 2

Electric flap motors are more quiet..  they drove jackscrews..  a very long piece of threaded rod that had a traveller that moved as the rod spun. Hydraulic pumps can make some racket, but it's comforting because you know it's working. Yes, Hyd units can drive the jackscrews also... You may hear them running for driving the boards as well.

Answer 3

It is the operating mechanism at work which can be heard. The new generation airliners have a much quiter cabin interior, hence sounds are more audible as compared to the older 737, 747s etc.

Answer 4

motors moving them

Answer 5

Should just be the hydraulic motors you are hearing. They are either closer to the passenger compartment on the 767, or are not insulated as well.