In the early 1920's, I remember riding in what was called the "rumble seat" of a Pontiac coupe. The lid of the trunk when lifted up toward the rear, was the cushioned back of a seat below. It was fun riding in it on a sunny day. I thought it was a new name, derived from the fact that it was a bit noisy back there. I didn't know it was a relic from horse and buggy days.See definition #3
"Through the same cold sunshine, and the same sharp wind, my Lady and Sir Leicester, in their travelling chariot, (my Lady’s woman, and Sir Leicester’s man affectionate in the rumble,) start for home."

Webster's 1913 Dictionary

Definition: \Rum"ble\, v. i. [OE. romblen, akin to D. rommelen, G.
rumpeln, Dan. rumle; cf. Icel. rymja to roar.]
1. To make a low, heavy, continued sound; as, the thunder
rumbles at a distance.

In the mean while the skies 'gan rumble sore.
--Surrey.

The people cried and rombled up and down. --Chaucer.

2. To murmur; to ripple.

To rumble gently down with murmur soft. --Spenser.




\Rum"ble\, n.
1. A noisy report; rumor. [Obs.]

Delighting ever in rumble that is new. --Chaucer.

2. A low, heavy, continuous sound like that made by heavy
wagons or the reverberation of thunder; a confused noise;
as, the rumble of a railroad train.

Clamor and rumble, and ringing and clatter.
--Tennyson.

Merged in the rumble of awakening day. --H. James.

3. A seat for servants, behind the body of a carriage.

Kit, well wrapped, . . . was in the rumble behind.
--Dickens.

4. A rotating cask or box in which small articles are
smoothed or polished by friction against each other.




\Rum"ble\, v. t.
To cause to pass through a rumble, or shaking machine. See
{Rumble}, n., 4.