Interesting observation regarding filters, output voltage, and hiss

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Let me start off by stating that I am unsure whether this is normal behavior, or indicative of a potential issue with my Bartok.

I noticed a rather loud hiss coming from my speakers (left channel more so than right) that appeared to be coming from Bartok. My simplified system comprises of the following: Bartok (rca outputs) -> amplifier (First Watt F8) -> speakers (Audio Note AN-E/LX)

All impressions are with the material being played in pause mode (no actual music playing). Volume settings do not impart any change to the hiss, except when pressing the Mute button, which completely eliminates it. Otherwise, volume at minimum or maximum has no impact.

Steps performed:

  1. Swapping Bartok output cables - hiss present, predominant hiss moves to the right speaker
  2. Swapping amplifiers (First Watt SIT-3) - hiss present
  3. Disconnecting Bartok from amplifier - no hiss in speakers
  4. Connecting Bartok to amplifiers via a preamp (balanced connection into HeadAmp GS-X mk II) - hiss present, same characteristics

At this point I determined that the source of the hiss is indeed the dCS unit, so I began focusing on it.

Material played:

  1. Tidal MQA (DSD upsampling, M1 filter, DSD filter F1, output voltage 0.6V) hiss present.
  2. Tidal MQA (DSD upsampling, M1 filter, DSD filters F2-F4, output voltage 0.6V) hiss not present
  3. Tidal MQA (DSD upsampling, F3 filter, DSD filter F1, output voltage 0.6V) hiss not present
  4. Tidal MQA (DXD upsampling, any available filter, output voltage 0.6V) hiss not present
  5. Qobuz High Res (DXD upsampling, any filter, output voltage 0.6V) hiss not present

I then surmised this is related to DSD upsampling, so I continued my investigation (Tidal MQA and DSD upsampling were used for the below):

  1. Filter M1, DSD filter F1, output voltage 0.2V or 2V hiss not present
  2. Filter M1, DSD filter F1, output voltage 0.6V or 6V hiss present
  3. Any filter other than M1, DSD filter F1, any output voltage, hiss not present
  4. Filter M1, any DSD filter other than F1, any output voltage, hiss not present

So it appears to be a very specific combination of MQA material, DSD upsampling, M1 filter, DSD F1 filter, and output voltage of 0.6V or 6V for the hiss to be present.

Any thoughts on whether this is normal behavior, or I have a possessed unit?

And, finally, the frequency plot of the hiss (grey) compared to baseline for the room (red) when the hiss is not present.

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