Sound?

Rather than a sound... It's more like she could hear a repeatedly played track she said...

Though it seems like she can't recall what it is.

It's just a probability.

So she feels like she remembers the track and at the same time doesn't know the track's name for some reason...

Could it possibly have anything to do with her right arm...?

At the current stage, we can't say anything about a relation between her arm and the track...

But

Nobody seems to be coming back at all...

There's something we know for certain.

Hm?

That girl's right arm

has a modernization scar that doesn't look like it's new.

Stop that!