I've seen this too often on the 767s, it's only a matter of getting to the connection to tighten it, however getting to that connection, is time consuming. It's the same thing when we get info from the CA about the audio being out on one side of the cabin from X-Y...

From what I've been told from a few maintenance folk, it's from pax jamming overstuffed bags into the OHBs day in/day out and it jiggles the wire connections of the audio/lights.

I've seen this not only on AA, I've seen it on UA and DL when I've commuted on them as well, even on the newer RJs.