Can the sound produced by a commercial aircraft flying at 35000 feet be heard on the ground when the surroundings are quiet?
It doesn't even has to be very silent around you.
But because of the speed of sound, you will hear the aircraft later. Here is the approximate time, the sound needs to reach you:
Speed of sound at MSL: ~340m/s
35.000 ft in m: ~10660m
10660 / 340 =
That means you will maybe hear the aircraft but you are not going to spot it where the sound comes from.
Note that this is not an exact value, as speed of sound varies with air density and temperature, which both change the higher you are.