Real Dictionary

rumble
countable noun: A rumble is a low continuous noise.

rumble in American English
a deep, heavy, continuous, rolling sound
to cause to make, or move with, such a sound
to make a deep, heavy, continuous, rolling sound, as thunder
intransitive verb: to make a deep, heavy, somewhat muffled, continuous sound, as thunder
noun: a deep, heavy, somewhat muffled, continuous sound
transitive verb: to give forth or utter with a rumbling sound

rumble in British English
noun: a deep resonant sound
verb: to make or cause to make a deep resonant sound