Error, you need to install an application to configure the sound (pavucontol, alsamixer, ...)
the word correct is pavucontrol.
I use ArchLinux and last version the LXDE
Patch submitted here: https://sourceforge.net/p/lxde/patches/466/
I believe this issue is completely fixed in latest version of LXPanel - 0.7.0. Try it, please, and let us know if something is still wrong. Thank you very much.