tibook sound on 10.0.4

I got my sound back after a reboot, but it seems to disappear again inexplicably, usually when I've been using IE.

Has anyone else had this behaviour?
I've not had that problem with 10.0.4, but I do have problems when I plug in headphones. In both 9.1 and 10, plugging in headphones sometimes crashes the TiBook and sometimes kills all sound--even when I unplug the headphones.