No hiss here, dead quiet. I had my MPD3 connected via XLR (currently running single ended) and it was a black background to say the least. For your reference, I use a Cardas clear M power cable into a Running Springs Audio Jaco conditioner. The problem is likely elsewhere although I guess anything is possible with electrical components. Do you live in an area with difficult power delivery? Especially when summer is concerned, sporadic voltage fluctuations could trigger a number of anomolies. Peace.