No chime on dormant PB G4 Ti seems to work as expected

I have several Powerbook G4 Titaniums which I broke out of storage. I'm preparing them for donation.

None of them give any sound - no chime on startup and no blips when I adjust the volume (presuming a hard drive with OS X).

With some laptops, I have pulled the hard drive, so the best behavior I can observe is the flashing folder/? icon. Those didn't chime either.

I believe I have reset the PRAM (Alt-Option-P-R and holding down the power button).

I have reset NVRAM via Open Firmware with:

reset-nvram

set-defaults

reset-all

I have also reset the PMU by either lifting the keyboard and hitting that button in the top right corner.

For the Onyx and Mercury units, I see the same behavior, even after hitting a different button to reset the PMU.

What else can I try to restore sound?