Occasionally while I'm listening to something on my headphones I'll notice that the sound is coming out of my speakers as well. It doesn't happen all of the time. I am running Ubuntu 14.04 on a Dell Inspiron 15-3521. There are other questions about this same issue but as far as I can tell they are all on 12.04.
What I've tried
Manually muting the speakers in alsamixer as a temporary fix
Downloading gnome-alsamixer to use the headphone jack sense option, but apparently that doesn't exist anymore.
Any help would be appreciated
%% update 4/14/15
I found that when i'm having the issue, if I go to my sound settings and look at the output tab, it shows "play sound through speakers" and does not switch to "play sound through headphones" when I plug in the headphones.
When it is working properly, it does switch to "play sound through headphones"