I have an intel Imac dual-booting Ubuntu 10.04 and OSX 10.6. Both work fine, but sound is very quiet in Linux, even though the gnome volume control panel and pulse audio volume control panels are both set to 100%. I can turn the speaker volume up and it's fine, but then when I boot back to OSX the volume makes me jump out of my skin. Is there a setting I'm missing? If I turn the gnome sound pref volume higher then 100, it tends to distort the sound. (crackling)
I can give you two. First one is Pulseaudio sometimes is not your friend. On some rare systems it configures the wrong mixer. Open a terminal and run the command: alsamixer -c0
This will show your mixers. Ensure they are at proper levels.
Also you can install the alsa backports package. This may improve support for your card. install by running this command: sudo apt-get install linux-backports-modules-alsa-lucid-generic
Do not do the second if the first solution with alsamixer works. I hope I can be of help.