"Twangy" string

I just finished a dulcimer that has a very twangy-sounding middle string. Bass and melody sound fine. I though it might have something to do with the way I cut the slots for the nut and bridge, (ebony) so I cut new ones, but no change :-(

My dulci is 20.25" VSL and I have single 14 ga string for melody, 17 ga for middle and 26 ga bronze phosphor bass Is it the string gauge/VSL combination? The size of the sound holes? The wood (bocote bottom and sides, and curly maple top? The phase of the moon? Inquiring minds want to know!

Ed