Searching to solve this problem i found lots and lots of other problems that didn't quite sound like mine: My headphones/speakers jack seemed to have developed a loose connection for Lenovo T420 running Debian Mint. Sometimes it will stop (or not start) playing audio through the headphones, and fall back to playing through the internal speakers.
Except where otherwise noted, content on this site is licensed under a Creative Commons Attribution 3.0 Unported License.