I have a project, on my workbench, right now, that ticks when I apply power to it. Until now, I treated it as an odd curiosity that I might pursue some-other-time. Well, this post lit a fire -- so I rustled up a length of hose, and probed the board while powering it on and off. I traced the faint sound to a pair of SMD ceramic capacitors.
I have heard of ceramic capacitors behaving like microphones, due to a piezo response in the ceramic material -- which means it could also act as a speaker!
In fact, I found an article on it from a credible source [Kemet]:
Kemet Article: PIEZOELECTRIC EFFECTS CERAMIC CHIP CAPACITORS
(Singing Capacitors)
BUT, if this is what is happening in your case, then how is the sound being coupled into your audio signal?