Andy, welcome. You haven't given any details about your setup, but assuming that you're using an HT receiver with a an internal menu setting for the sub output trim level, you should try to set that higher(so that there's more voltage going out to keep the sub amp "awake")and then you'd lower the level control on the sub itself to compensate for this and keep the same overall sub loudness level.

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Enjoy the music, not the equipment.