You may have a bad tube. When I had an issue with some buzzing it turned out to be a bad input tube. Which was strange since it was a brand new Gold Lions 12AX7 used for about a week but these things happen. Now the Taboo is back to its dead quiet self. I would start replacing tubes (assuming you have a 2nd set) to identify a possibly bad tube.
quick question for you all, do any of you hear any humming/buzzing/ANY kind of noise or sound when you have headphones (any headphones) connected to your Decware gear when NO music is playing??? Do you find this noise normal? Abnormal? Does it not bother you much once music starts playing if you have any noise at all?