What's a sound that used to mean something and now means nothing?

I used to navigate by the fog horn at the mouth of the harbor—three blasts, pause, three blasts. It had a language to it, a grammar you could read in your sleep. Now they've replaced it with some electronic bleat, and I catch myself listening for the old one like a dog waiting for a door that never opens. You ever have a sound like that—one that used to tell you something about your place in the world, and now it's just noise?