Hi... I just got my hands on a Sunn 200S. And it has buzz going on even when there is no input. It is also volume independant. Actually it only gets louder when I turn up the EQ. Turning up/down the volume has no effect. Any ideas? Also it only has a 2 prong powercord and I would like to convert it to a 3 prong. But where does the ground pin go? I am guessing straight to the chassis. But si there something special I need to know when doing this kind of conversion? Thanks!