Here's why:
* It describes an action: "Rumble" refers to a low, continuous sound, like thunder, a stomach growling, or a car engine.
* Past participle form: "Rumbled" describes the action of "rumbling" in the past.
* Used as a verb: "Rumbled" can be used in various ways:
* Past tense: "The engine rumbled to life."
* Past participle in passive voice: "The secret was rumbled by the journalist."
* Part of a verb phrase: "They had been rumbling for hours."
Let me know if you'd like to see more examples!