Wait, everybody doesn't hear music in their heads, all the time, like constantly? Ha ha.
When my PTSD (or my MS flare, who knows) started last year, that was one of my complaints. I couldn't stop hearing music. I told this to my PCP at the time, who I've since fired because she told me my thyroid symptoms were in my head. She had no answer and I never really followed up on it. I did go to the ear doc, who said I had an auditory processing issue. Since I knew my ears were okay, I just put it in the "another brain thing" pile and move on.
Yesterday I was in the kitchen flat out dancing to a song that keeps being played on the radio, but was only playing for me. I constantly check my phone thinking I've heard it. This doesn't happen so much now that I have a specific song for it (the Muppets Mana Mana song). I think I hear my daughter calling me, nope. I hear odd stuff all the time that isn't really happening. And then when people do talk, I don't hear the correct thing, it's all jumbled up. I have to ask people to look at me when they talk so I can read their lips. My hearing is totally perfectly fine, my brain just can't put it together right.
The more stressed one is, and the less sleep there is, the more apt this will be. I think one of the good ways to deal with it is to actually play music. Give that brain something to listen to.
Now if you hear somebody whispering to you, that's ghosts! That's totally different