ZP3 muting

[enterpryse]

I have 2 ZP3 preamps.

The second was a replacement because the first would mute its input randomly after 10 minutes or so after selecting it.

Once re selected it mostly would be fine for the rest of the listening session.

Now the replacement ZP3 has started to do the same thing.

Bit of set up info:

• Cycling through the input selector doesn't always restore the audio.
• It's does this on any input.
• The selector LED stays on even when it's muted/deselected itself.
• Same power supply cable used while testing both units.
• I'm using RCA in and XLR out.
• Tones are in bypass.
• Response flat.
• Trigger not used
• Input is fed from a FIIO K11 R2R unbalanced or PC (I've tried removing inputs from the PC as a test but made no difference, I was considering different earth potentials or leaky/noisy PC PSU).

Also, there are two distinct relay clicks when selecting an input. The first clicks coincide with pressing the input selection button and the second about 2 seconds after that, which unmutes the audio (is this normal???).

On some occasions, when it muted itself, cycling through the inputs back to the one I was listening to (using the front panel switch) I get a very short burst of music before it mutes again.

I can't have two faulty units, at least what's the chances??

On a positive note I don't have any hiss and am very happy with the sound.

I posted this on Facebook but I seem to be the only person experiencing this :-(

Ideas anyone???

Thanks in advance.