We cannot control what comes to us spontaneously during meditation. Our focus is the volitional activity, the meditation practice itself. When we practice with a free mental attitude, we create a sort of mental freedom within us, where impressions, feelings, and fantasies can flow freely.
The meditation sound should be adjusted to the spontaneous activities of the mind. When the meditation is more on the silent side, we repeat the meditation sound more subtly than usual. Attempting new ways of repeating the sound will involve increasing our inner freedom, beyond what we are usually capable of. We should not be restricted by habitual patterns of reaction. The challenge is to meet the new situations with an open mind.