It seems that there's an issue with the dulcimer and not the string. I changed strings three times and continued to have the same problem. It was quite inconvenient as I had a concert Tuesday night. I have another identical McSpadden (although with a contact mic, not a pickup). I had it strung with only three strings, but added a fourth for the concert. I was afraid to put on a whole new set so soon before a performance, especially since the problem I am having only occurred after a string change.
Between the age of the strings and getting used to the contact mic, the sound wasn't quite as bright and I had to make some changes in the music. A pickup only amplifies the strings, but a contact mic amplifies everything. I normally do some "tapping" like guitarists do, but with a contact mic, all one can hear is the tapping and not the pitch, at least when playing harmonics.
I was pretty nervous owing to the last minute changes, but the concert was, I'm pleased to say, a success. The program consisted of my own songs, set to the poetry of Amy Levy (from my album that streams in all the familiar sources) and an encore of Simple Gifts. The vocal was by Victoria Vargas, I'm not a singer.
I'm also not a builder and will need to have my instrument evaluated and, I hope, repaired. I love it dearly and would hate to have to replace it.
Thanks for reading and have wonderful lives.