[CAUT] Puzzler

[Susan Kline]

 From yesterday ...

I put in a long service day on a neglected and much-played
Mason & Hamlin BB, about ten years old. When I first started
pulling the action out, I heard a soft repeated Eb7, sort of
like a very loose bobbling hammer, but not quite. It got
softer and faster till the sound disappeared, like when a
ping pong ball is bouncing, and then coming to rest.

I said, "oops", and wondered if some action trouble had
a hammer doing a dance in the high treble -- but the
hammer was down, just like the others. "Go figure",
I said to myself, and carried on.

A couple of quiet hours later, with the keys on a little
folding cart six feet from the piano, and the action reversed
(hammers out) on the bare keybed to get teflon on the
knuckles -- there was the same sound again. Eb7. Nothing was
near the Eb7 string.

I never have heard that sound from a piano before, let alone with
no action and keys involved.

What was it?

(P.S. I figured it out ...)