Are you sure it's "Rumble"? I was thinking that it's "Ramble"--
Walk for pleasure in the countryside, typically without a definite route.
A walk taken for pleasure in the countryside.
verb. wander - roam - rove - stroll
noun. walk - saunter
It sounds like someone on the Japanese staff wanted a non-Japanese word for the name of their tribe, so they looked up the English translation for 迷う (or a similar word) and thought "ramble" sounded good. "Rambling" isn't quite what I'd say the Wanderers do, but it's close enough and certainly fits one definition of the Japanese word. Kind of like how a native English speaker might say 涼しい instead of 冷たい to refer to the coldness of water. Both mean "cool," but have different uses.
"F*** you, I'm a goat." -Yohn