I have two DACs going into the C2a, a Musical Fidelity V-DAC and an AudioQuest DragonFly Red. As an aside, I like the V-DAC much better because of its spaciousness and tone. The V-DAC is connected by optical, and with headphones there is zero buzz. So, it seems to be an interaction with the Yammie? Because the C2a with headphones is noise free, and the DACs straight to the Yamaha are noise free. Thanks for your help yet again, Paul.