Well, I've checked the whole string here and decided to chime in with some advice. First, you might try to lighten up as in hold your strummin' 'wing' up some so as to sort of float across the strings. Also, do you strum across the strum hollow ( that little dip at the pointy end where you attach your strings ) or the widest part of part of your dulcimer? I usually strum over the wide part. A word about tape recorders, they're not always the best way to judge sound. Too many variables i.e. room size, speed differences between tape players etc.

Hope this helps some.