Yeah pretty much the only way to set the "perfect" motor height is to listen to it. It's fine tuning basically. If your gun can fire then it's set "about right", enough that the motor can spin and contact the gears and all that.
Basically tune it so it's the least noisy. It won't be perfectly quiet but will instead be less noisy. When you do this you'll want to do about quarter turns and also remember how it sounded the last time it shot so if it gets noisier again then you can turn it back (noise can come from it being too high or too low).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE