[pianotech] What's causing this vibration?

[Douglas Gregg]

John,
I had a small Setengren  baby grand with a very similar problem.I had
sold this piano and  guaranteed it, so I had to find it. But this one
was intermittent and seemed to be worse when there was high humidity.
The owner mostly played after midnight when it was really quiet and he
was very sensitive to this noise. I was convinced it must be related
to the soundboard. It never seemed to be very bad when I was there so
I took the piano back to the shop and put a humidifier near it. It was
subtle and I could not find it. I even turned it upside down and tried
to wick glue under any possible loose ribs or the rim. I was all over
this thing. I thought it had to be gone. I returned the piano to the
house and it was OK for a week and then came back. This time, I was
there when it was making noise and it was loud enough to track down.
It turned out to be three screws in the back action that had loose
washers hanging on them. I still don't know what the screws were for
but the washers had done it. I removed the washers and it is fine now.
The humidity must have just been a red herring.
I spent about 12 hours on that one.

Doug Gregg

Message: 1
Date: Fri, 9 Mar 2012 18:59:30 -0500
From: Rebecca and John Silva <misc at rjsilva.com>
To: "pianotech at ptg.org" <pianotech at ptg.org>
Subject: [pianotech] What's causing this vibration?
Message-ID: <6DA1BC72-C295-45AB-BC4D-AB9680FF88A2 at rjsilva.com>
Content-Type: text/plain;       charset=utf-8

Hi,

When playing a particular note on a piano I saw today (Baldwin L) a
harsh vibration would sound. The vibration would only happen for a
moment (1/4 second?) even while the note continued to sound, it was
about 1/2 the volume of the note and only happened when playing hard.
I worked with the owner for about an hour trying to figure it out and
we were only able to determine it is based on pitch?if I detuned the
note it would go away, and if I detuned the adjacent note to the
offending pitch that new note would cause the vibration.

I looked at everything I could, ensured every part/screw I could see
was not loose, tapped on the bridge pins, and tried to figure out
where the vibration was coming from.

Does anyone have any suggestions of where to look? Any common but
elusive offenders? Two highly regarded technicians in the area were
also apparently unable to figure it out.

Thanks!

John