Me too with Dell 9400. Amazing machine btw :P
Seeing bug #410948 I've found a workaround which seems to be working pretty well for me. There are some variants around, but this is the one that IMHO is less intrusive from a system point of view but needs to be setup at each user:
===== This is only info recopilation =====
======= Credit to Daniel T Chen ======
1) see if you have the file ~/.pulse/default.pa
if not, just get a copy from:
cp /etc/pulse/default.pa ~/.pulse
2) Now, edit ~/.pulse/default.pa
goto line 55 which should be:
and modify it to be
load-module module-udev-detect ignore_dB=1
3) now go a bit up and uncomment the line
and modify it to be:
load-module module-alsa-sink control=PCM
4) stop any apps playing sound
5) kill pulseaudio (pulseaudio will respawn by itself):
6) run alsamixer at a terminal and make sure you have Master and LFE levels to about 50 or even 100 if you want loud range. Navigation inside alsamixer is: left and right arrows select channel, up and down arrows modify channel level, M mutes/unmutes a channel.
7) Move gnome sound volume slider: you'll see that now Master and LFE are not touched and that the slider only applies to PCM channel.
8) Go rhythmbox or whatever and play your favourite songs or whatever. Play with the gnome volume slider and see if everything is just OK.