While Bella indulged her mad compulsion to go even farther afield, and last night to master the neighborhood of 16th and T St., I wondered about the subterranean rumbles. Freeways? Trains? Everything is BNSF these days, but still, Sacramento folks prefer the historic usages. They allow horns at night, so you can hear the Union Pacific trains for miles and miles, but you never, ever hear the Southern Pacific trains until they are right on top of you. But these rumbles? What are they? They're everywhere! It's a mystery.