Noises of various kinds (clicks, rattles, buzzes and squeaks) can be one of the most unbearable annoyances for the pianist and must be fixed. If a piano has been stored in a very dry environment (next to a fire place for example), the felts in the action and keys can dry out and disintegrate over time. This not only causes regulation problems but can also lead to annoying clicks that make playing the piano unbearable.
If you’re piano clicks loudly on every note, it’s possible that hammer butt felts in the action have disintegrated. The causes the jack to slam against the wood of the hammer butt rather than felt after a note after a note has been played. This can be an intensive job to fix due to the time consuming nature of re-felting 88 hammer butts. If it’s the only issue with an otherwise good quality piano it’s very much worth doing – with the price of felt included I would charge £250 for a full replacement of every hammer butt felt (although it would be much cheaper if only a few have disintegrated)
However, If the hammer butt felts have dried out and disintegrated it’s very likely that the balance rail punchings and the back rail cloth have also dried out and crumbled away to various degrees. If the keys are different heights then this is likely to be the case. Replacing the balance rail punchings/washers and the back rail cloth – and cleaning the entire key bed – is also important as any dry crumbs from the disintegrated felts can be catastrophic to the pianos performace and cause different key heights and sticking keys. In the case of the back rail cloth, if you can imagine the very back of the key resting on a collection of cloth debris rather than a clean, even strip of cloth you can see why even a slight difference in how the back of the key sits can cause the front of a key to be raised or lowered.
Another possibility for clicks on every note is that the hammer rest rail is either loose or has come off. This would cause the hammer shanks to click against the wood of the rail (rather than felt) after a key is player and the hammer falls back into resting position.
In the key bed, a cause for clicks is the key bushings being worn out causing the loose key to rattle against the front and balance rail pins, although this is lesson common cause of clicking.
One issue I’ve occasionally seen on older uprights, is the capstan screw being exposed and clicking against the wippen when a key is played – this is an easy fix as a thin layer of felt (with minor re-regulation) over the capstan can fix the issue within minutes.
The common theme here is of wood hitting wood where it should be hitting felt or cloth. If the humidity of the room is kept at reasonable levels (40-50% is the sweet spot) this can be avoided long term as of the felts and cloths in the piano action are designed to withstand years of aggressive piano playing. I’ve seen instances of pianos kept next to fires where the felts dried out on the side that was closest to the fire and the other side was fine. Very dry air destroys pianos, so please be careful where you keep your piano!
- – Richard Lidster, Sheffield Piano Tuner