I have been browsing the forums, and it appears a few people have had this problem. But as of yet I haven't seen a solution.
I have tried editing my ~/fluxbox/keys.conf, and added this:
XF86AudioLowerVolume :ExecCommand amixer set Master 5-
XF86AudioMute :ExecCommand amixer set Master toggle
XF86AudioRaiseVolume :ExecCommand amixer set Master 5+
Yet that doesn't seem to be changing anything. I am running the latest version of LM fluxbox 9, with most of the settings pretty much as they were out of the box. Anyone have any idea?