Annoying partial tones in piano

I have MS 2.0 and FluidR3Mono_GM.
dm7-5.mscz
I had this sequence in a score and I tried to find the wrong note in the score among lots of instruments. Finally I found out that it was in the piano sound. The left hand D note creates an annoying partial tone (third partial or A). On the beat it sounds like Dm7, but the chord should be Dm7-5, as the notes show. This could be an unfortunate sum of lots of things, like my sound card and my head phones and you might not hear what I hear. I exported it to a wav and the partial tone is there, too.
Of course, this happens sometimes with real world instruments, too.