I serviced a piano for an individual who was told by a piano technician that their soundboard was "going bad" and would need to be replaced to correct the buzzing they were hearing when certain notes were played. He quoted about $3,500 for the repair. He offered this suggestion after spending some time working on the strings.
When I arrived at the piano, there were many chips in the gold plate where the bass strings connected to the plate, or at the hitch pins to be specific. It was apparent that the technician tried twisting the strings and did quite a bit of damage during the process. I advised my client that I thought I could correct the problem by twisting the strings again. When I did, I found that the previous technician twisted them in the wrong direction which was why the buzzing did not go away. I gave them all a proper twisting and the problem was resolved for a fraction of the cost of a new soundboard. It was a happy day for both of us.
Bass strings within a piano are comprised of a steel core wire wrapped with copper which makes them easy to identify. You may find that one or more of your bass strings makes a buzzing sound, as if something was making contact with the string that should not be. Often it will produce a sound similar to what you would hear if you rested a paper on the string, then struck the key. It can become quite an annoyance.
If you experience this and do not see any foreign objects making contact with the string then you have a legitimate buzzing string (congratulations). Usually the cause of this misfortune is the copper winding beginning to loosen. If the problem is present in just one or two strings, it can often be resolved by a technician during tuning without adding significant cost. Other times it requires other methods of repair or replacement of the string.
If you live in Boise or nearby and have buzzing bass strings that need diagnosis, contact me for more information.