[hpsdr] Audio output noise

[Mike F]

My Mercury based system (Mercury, Penelope, Metis) has developed a 
problem.  Operated the system and then didn't turn it on for about 5 
days.  When I turned it on everything appeared to be operating, but when 
I applied power both the speakers and the headphones had a noise that 
sounds somewhat like digital data.

The noise continues when mute is pressed.

The noise continues when in transmit mode.

The noise condition doesn't change with changes in the volume, even when 
the volume is at 0.  This is true of both the master volume and the 
rx1/2 volume controls.

The system is fully functional.  When operating, signals can be heard, 
and change level with the volume control.  The noise is still present.

I tried to record the noise with the volume turned to 0.  The recorded 
file had no output, although it was the length of the recording period. 
  I do hear recorded output with the volume up but I believe that it is 
the band noise, without the described problem.

I tried a different power supply.  Nothing changed.

Cycled power and rebooted the computer, no change.

Reconfigured PSDR to default values. No change.

Haven't successfully tried a different computer.  Tried psdr 2.3? but 
couldn't get by the firmware check.  Tried 3.2.9, problem same. Present 
PSDR 3.2.24

Just prior to the problem Windows 7 did an update.  The system is based 
on the Intel ZEON processor.

HELP!