String noise

I have a Ron Ewing Dulcimette that I am working on a special project with.  Unfortunately, the middle string has a "tinny" or "twangy" noise -but only part of the time.  I put new strings on, but that didn't make any difference.  The middle string appears to be the same height as the other two.  I really can't figure out what the problem is.  Has anyone here had issues like this?

Thanks for your help!