I have a 30 year old upright piano withan iron frame. It had been neglected for probably 10 years. 6 months ago it has been repaired and tuned. The action had to be cleaned and pieces of felt and bridles had to be replaced after some mice had made a nest in it (did I mention that is was neglected?). A few months after it was repaired we moved the piano to another room in the house and after a resting period there it became audibly untuned and 'noisy'. 6 weeks ago it was retuned to concert pitch. Now I have the feeling it is already getting slightly off and 'noisy' again.
With 'noisy' I mean the notes have an unpure tone, a lot less full then they were. ALso harmonies tend to sound strange. Also, when I use a guitar tuner to measure pitch, all pitches of all keys have shifted, as a general tendance, a little flat.
As I don't have perfect pitch, I wouldn't think I would be able to hear this general lowering of all pitches, which keeps the relative intervals between the pitches intact. I was triggered to measure the pitches of my piano because I had the feeling tone wasn't what it used to be when it was just tuned and it had a noisy feeling. So now my theory is that this effect is generated by only some of the strings of the groups of three per key, getting out of key. Could this be possible?
Is it normal for a piano to get out of tune this fast? Is it a warning sign that my piano behaves this way?