I've just run into something I've never encountered before. I've got this
big orchestral multitrack project going and in this one little spot, there's
a weird burble in the french horn. (The orchestral tracks were made by
internaly recording off high quality midi)

At first I thought, damn, the track got corrupted somehow. But soloing the
track it sounds find, while in the mix it sounds exactly like what happens
when there's an audio glitch. I A/B'd it in combination with other tracks
and lo and behold, when it's combined with the vocalist's track, which is
what the whole orchestration is being built around, in this one spot this
weird thing happens. Both tracks sound fine independently.

Any suggestions as to what possible cure there might be for this?