Was it in Morse code? Could have been a extraterrestrial in disguise or maybe just wanted breakfast and was pissed you weren't taking his order.

Once upon a midnight dreary, while I pondered, weak and weary,
Over many a quaint and curious volume of forgotten lore,
While I nodded, nearly napping, suddenly there came a tapping,
As of some one gently rapping, rapping at my chamber door.
"'Tis some visitor," I muttered, "tapping at my chamber door —
Only this, and nothing more."
The Raven
—Edgar Allan Poe