Vibrator as Diagnostic

[Newton Hunt]

I know that sound and I have not found it's source on occasion.

I did find a plate brace that hummed with a certain note.  I
discovered this by banging the brace with my fist trying to find
something else and low and behold the exact sound was there.  I did
find that the rebuilder left a small screw wedged under a bridge which
caused the other vibration.

(sigh).

		Newton