Try disconnecting the Modi as you may be getting noise passed through from your computer. If you are still hearing the noise then I would try removing and reseating the tubes. If that doesn't work I would contact Schiit. As to the know it will be quite warm. Check to see that it has not been pushed all the way in by using a small hex wrench. By making sure it is not touching the inner nut there is less thermal transfer.
8/20/14 at 11:41am