Thank you for responding. I did try to see if I could isolate the problem to one string, and I could not. I think I will try different strings, though, and at your suggestion, I will use lighter gauge ones. 

I don't think the instrument's sustain is a problem with the strings. You might try a lighter gauge string just to see if it changes anything, but it may just be an instrument that has a longer sustain.

I'm trying to get back into playing my dulcimers. I have 3 that I've had for years. I've restrung all 3. One of them, built by a well-respected luthier, sings too long. That is, the sound goes on for a good 8 seconds after my hands have left the instrument, and it's distracting. When I put my hand on the wood, the sound stops. I don't want a choppy cut-off, but this is too much. I suspect I've done something wrong with the re-stringing. Any ideas? The other two don't do this. I have had the strings for a while, but they were in their original envelopes.