Use cmevoli's solution

http://unix.stackexchange.com/questions/72131/detecting-x-session-in-a-bash-script-bashrc-etc/338862#338862

dotfiles/bash/main.bashrc

@@ -271,7 +271,7 @@ export GIT_PAGER='less -S'
 export GVFS_DISABLE_FUSE=1
 
 # disable the terrible beep sound (only for X; for tty?, blacklist pcspkr)
-[[ ${!DISPLAY[@]} ]] &&  xset b off
+xhost >& /dev/null && xset b off
 
 # get rid of those .pyc files once and for all
 export PYTHONDONTWRITEBYTECODE=1