You made an interesting comment about earthquake sound. I've been in the big Los Angeles ones, and the Northridge quake we were only 1/4 mile from the epiceter. For several months people very close to the center of the epicenter, we would hear an enormous rumble coming out of the ground, which was aftershocks. The odd part was you would think the sound would occur after or during the ground shaking, but this would always occurs seconds prior to the house shaking. WE finally go used to the sounds, which we would seriously jump up and head for the door everytime. It was almost a deafening rumble, and preceeded the house shaking by about 3-4 seconds. The epicenter of the Northridge quake was about 6-7 miles deep, and the rumble from that was so loud, you could not hear yearself. Deep ground noise can be very loud and rumbling. As far as a aircraft emitting a rumbling noise, some helocopter blades really emit a thunderous whapping noice, and also old reciprocating engine aircraft(not jets), also emit a very thunderous rumbling engine noise.