Emulator galvo gains

So.... one of my beloved emus seems to move less far for the same input as the other 5 units. Since I don't see any gain adjustment pots on the board, and the problem seems to occur with multiple logic boards, could this be the galvos themselves? I also notice this particular unit makes a lot of noise on certain patterns (the double musical note pattern seems to be one of the worst, probably because of its complexity). The noise seems to be coming from the mirrors themselves, not the galvo, almost like they're out of balance or something.

Any ideas?
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