I'm lying on a large roundish rock/boulder, face down with my head to one side, ear pressed to the rock. It is not cold. I hear a deep, thumping sound, like a slow heartbeat, in a regular rhythm. This goes on for a long time until I drift back into un-dreaming sleep.

I'd attribute this to the trains that run by my building if not for the fact that they are always accompanied by a loud screeching noise as they go around the bend. So if the noise appears in my dreams at all, it generally appears as "train", or occasionally "predatory bird". The underlying repetitive thump is virtually inaudible unless you lay on the floor. Maybe I was just in a different sleeping position.

Anyway, there you have it. I won't speculate on the meaning except to say that calling me an earth-hugging liberal wouldn't be too far off the mark.