Shorting RCA inputs

[Utopia]

My Crack buzzes with my Beyer T1 if I turn up to volume to perhaps 80 % of max (which I would never do listening to music). If I disconnect the interconnects from the RCA inputs I still get the exact same noise. However, if I short the RCA inputs, the amp is dead quiet even at 100 %.  I don't know quite how to interpret that. Is the source of the noise outside the amp? And do the RCA inputs pick up noise even when they disconnected?

[Paul Birkeland]

My Crack buzzes with my Beyer T1 if I turn up to volume to perhaps 80 % of max (which I would never do listening to music).

That's kind of the end of the story.  If that's an insanely loud listening level, some noise is to be expected.  (Remember, signal to noise ratio is just that: a ratio.  If you crank up the signal to an unreasonable level, the noise will rise also)

If I disconnect the interconnects from the RCA inputs I still get the exact same noise. However, if I short the RCA inputs, the amp is dead quiet even at 100 %.  I don't know quite how to interpret that.

What's the noise like with a source plugged in? 

The results of this tell you that you have a quiet amp, and some noise in the environment.