I have a Knabe Ampico grand which was restored almost 20 years ago.
In December of this year it was getting a heavy workout playing all
my Christmas and seasonal rolls.  After several hours of playing,
during reroll, I began getting a "howl" from the region of the
spoolbox transmission.

After removing the covers, I used a light oil and put a few drops on
every bearing on the transmission frame.  The Ampico/Amphion has oil
holes for most of these.  After working the transmission by hand for
a bit after oiling, my howl went away.

My point in this message is that the mechanical parts of these
instruments will run better with a little maintenance, especially if
it has been awhile since being restored.

Bob Conant