Nuforce STA200 issue. Rumble every couple minutes

The STA200 is an incredible amp, given the " proper system " it is paired with, and of course, the $499 selling price. People are giving them away it seems. 

@kray, it was designed to work with a passive preamp. @Mesch, it is not the perfect amplifier ( point me in the direction of " the one ", please ). Knowing it’s limitations, I bought my 1st one, and based on how much I enjoyed it, I quickly sold off locally, several other amplifiers I had in my large amp collection ( Mc 2105, Son of Ampzilla, Bedini 150, Hafler 200, B&K ST202, and a few others that I enjoyed,  and had good reputations. These were all up to spec, and they all had upgraded, heavier gauge power cables hotwired into them ( not a joke, when I tell you they improved greatly from this tweak alone ). I bought 2 more, to vertically biamp a pair of Signet SL280ex....an awesome system. I still have the speakers, but sold the two of the STA200’s, because I was down to one system ( with my Lascalas ), and felt someone else should enjoy them. I will keep my original STA200, as it takes up no room, and for what it does, it is a keeper. My best, Always, MrD. Enjoy !