All, A bit more advice required - I have setup (below) and if listen to anything above the volume of -20 (let alone reference of 0) on the amp the air / floor vibrates noticably. The white noise used for the setting the sound levels (I do have a sound level meter) it's fine with no vibrations of any kind. I have tried with the sub off and removing the centre speaker and it still happens. I assume it must be something to with the front missions (753's). I have spiked them to avail. I sit about 12ft away from them (this is also set in the amp). I have played with the cross over frequency and this have some affect but nothing really noticable (I could just be paranoia). The amp is also set to "LFE" only not "LFE and Main". Give us a clue!! Thanks, Rob.