(MAY BE OFF-TOPIC) Muse Sounds, for no apparent reason, plays a long loud dissonant chord where silence is indicated in the score.

I'm writing a symphony and came across this problem.
When I play it back from the very beginning, or even from any given moment, I hear a long loud dissonant orchestral chord which goes on indefinitely, even though nothing like that is written in the score. (A few dissonant chords are written but not everywhere and they don't go on till the end of time!).
This is part of a copy of the score which has the same issue (the whole score contains the 1st, 2nd and part of the 3rd movements; this copy contains only the 1st and the 2nd, and the chord is slightly different). What is going on here? It wasn't there initially.