Please check whether the level to be preset for the subwoofer channel in the loudspeaker/bass management of the feeding device (sound card, DVD player, receiver) tends to be set to a rather high value of about + 4 dB to "maximum".
The higher this value is, the more likely the subwoofer is to kick in because it is assigned a stronger signal. Is the slide switch on the back of the subwoofer also in the middle position "Auto"?