Yep - definitely a bad sound chip / circuit / jack on the 1Ghz board. I swapped in into the known good body of the 1Ghz, and... no sound at all.

i then put the working 867MHz board into the 1GHz body - and sounds works properly.

I now have a perfectly functioning 867Mhz Ti powerbook, 1GB RAM, running 9.2.2 and OSX 10.5.8.

That overclock stuff looks interesting / not too difficult. Will check it out when I get a bit of time & report back any results.