I'm quite embarrassed to ask this, as there's quite a bit of info out there, but I don't seem to be able to stitch it all together.
Basically, here is a new Toshiba laptop running ubuntu lucid. Everything works like a charm, apart from a microphone jack, which only produces very low level noise.
Sound output is OK, the problem is only with the input.
The microphone jack itself is fine, since it works under windows.
The pulseaudio server doesn't seem to mute the mike.
I'm at loss as to where to even start looking into how to fix this, and will very much appreciate any suggestions.
EDIT: Installing the
linux-backports-modules-alsa-lucid-generic (as suggested here: http://www.linlap.com/wiki/toshiba+portege+r700-r705) alleviated the problem. Now the internal mike works just fine, the mike jack sort of works but the noise level on the jack is still very high.