Comment 7 for bug 109457

Not sure the duplicated bug is exactly the same, but anyway my problem is best described here by Premier, and it is still unresolved (I have it on Kubuntu 9.04 Jaunty and on Gentoo). As I have a Sigmatel Audio Card with an Intel HDAudio chipset too, it may be related to this particular model/family.

Here is a shorter alternative to the script above.
For example if using xbindkeys to use dedicated audio keys add:
=== CUT ===
"amixer set Master 4dB- > /dev/null ; amixer set LFE 4dB- > /dev/null &"
  m:0x40 + c:122
#or Mod4 + XF86AudioLowerVolume

"amixer set Master 4dB+ > /dev/null ; amixer set LFE 4dB+ > /dev/null &"
  m:0x40 + c:123
#or Mod4 + XF86AudioRaiseVolume

"amixer set Master togglemute > /dev/null ; amixer set LFE togglemute > /dev/null &"
  m:0x40 + c:121
#or Mod4 + XF86AudioMute
== ENDCUT ==
to your .xbindkeysrc.
(I've used the "Windows" key above, xbindkeys wouldn't override kde default shortcuts.)