I work more with the visual side of the industry, but I do find myself having to do audio from time to time. It's part of the duty of the kind of work I do. Since I don't consider myself a professional when it comes to audio, I'm going to pick your brains on this one. I have pretty sensitive ears, and others have told me they can't hear the problem I am talking about. That said, I'm hoping that some audio engineers would be able to explain this one to me, since you all likely have sensitive ears as well.
I've been able to isolate this problem to choral music and sometimes strings, more notably recent music that was recorded digitally. I can only attest to this problem through Spotify, so perhaps this could be a problem with the way they process music recordings.
Here's the problem. If you listen closely to the examples I have posted below, you can hear an approximate 27Hz in-and-out sine wave in the overall recording (not the pitch frequency of 27Hz). This is most prominent where the dynamics of the music are louder. You may need headphones to hear this more easily. I'm wondering if anyone else can explain this, or if anyone else can even hear it... Maybe it's a hardware issue on my end?