Today I turned the amp on and literally almost fell on the floor - the speakers exploded with noise! The DS is connected directly, no pre-amp in between, but when I tried to reduce the volume using the DS screen nothing happened - the digits ran down, but the cannonade remained deafening and shuttering. The quickest solution was to turn the power amp off and think.
Then I switched the DS attenuator on (it worked) and tried again - noise. I checked other DS inputs (the default is the Bridge) - noise. Power cycled the DS. After it booted up noise. Removed the Bridge - no noise! Aha, that must be the Bridge! Connected a laptop to the USB input - the DS plays OK. No noise from other inputs.
Power cycled again with the Bridge in - noise. Rebooted the Bridge from the command line - noise (just changed in the tone). Tried to play something through the Bridge - no changes, noise.
Removed the Bridge again. 10 seconds of silence, then noise from any input. The loudest is from the USB. On other inputs the noise can be quieter, or come like a wave, or begin in one speaker and move to another, etc. Installed 1.2.1 - noise, re-installed 1.2.3 - noise.
Checking the inside of the DS did not show anything obviously wrong, like loose cables, burns, hot spots, short circuits, etc.
Just in case, the DS (the upgraded PWD II, which is in turn upgraded PWD I) was working fine for months.