As the question suggests I have the Audiobox USB96 25th year edition. I noticed this by chance. I have NO cables plugged into the inputs. Gain all the way up to max. I can hear when I tap the case, almost like there is a microphone inside the case. At about 2 clicks from max I suddenly hear white noise and the tapping sound heard through headphones pretty apparent. 3 clicks back from max it's still there but much less volume.