It was like a rumbling sound, maybe like a freight train(Even though Ive never heard a freight train before LOL) good thing the flat screen TV that hasn’t been mounted on the wall stayed put..our dogs, not a peep out of them, didn’t give us any warning. My sisters upstairs neighbor has a Boxer, he got so scared that he ran downstairs to the backyard and puked poor baby..guess some dogs just can’t take it