Broken, missing or old strings
Broken, missing strings can put stress on the hammers when they are not hitting all the strings they are designed to hit. And in certain places missing a string can cause the dampers to not damp the sound properly. I carry replacement wire and a variety of universal bass strings. Sometimes the old string can be salvaged. Sometimes it's better to put on a new string. A custom-made bass string might be better than a universal bass string. Let me check it out.