Here's to Good Friends. Tonight Is Kinda Special.

The other night, I was awakened at 3:19 a.m. by unexpected noises.  It kept repeating, so I couldn't fall back asleep.  Once my brain was fully awake, I recognized the -- shall we say "rhythmic"? -- nature of the sound.  (Then I really couldn't fall back asleep.)

I thought new neighbors had moved in upstairs, because I had never heard that sound before, for the entire year and a half I've lived in this apartment.  The apartment manager, though, says that no one will move in there until January.

Where did the noise come from, then?  Could it be from next door?  I know a college-age couple lives there, but, as I said, I'd never heard that nature of noise before.  You'd think they'd be going at it like a couple of college kids.  Why did I hear them that one night only?  Maybe they were celebrating graduation?