Funky looking subsonics in vinyl rip

Before I filtered out the subsonics in this needle-drop (a dance compilation 12"), I thought I'd look at them.
We can see in different songs the tracks have differing sharp high-pass filters applied already, the kick-drum only extends down to 30hz at most.

But something funny here in the frequency analysis (16384 FFT bands for this resolution):


There are interesting repeating shapes that happen in different songs and have no correspondence to the musical information. I thought of passing cars or something like that, but that doesn't seem to correspond.

Sony direct drive turntable with quartz lock, I wonder if it's from the TT; I'd have to do another rip to see if it's in different vinyl, but I've never noticed this before.

Some interesting mystery art below 30hz...

With this inspiration, a person could probably write a program to make some cool subsonic picture or messages and add it into their music. A watermark easy to remove but also easy to see.

Soon to be gone though:

 

Dust cover on or removed? I have had some odd subsonic resonances with various dust covers. I have also had stands or cabinets with odd resonance points. If you monitor through headphones while recording do you see the same "ghosts"? Or maybe you are already using headphones, in which case, nevermind my post.

 

I'm working on stuff ripped two years ago, but I would normally turn the volume down or off and pull off the dust cover. I think I'll have to pull the record back out and see if they are in the source material as I believe they are. Just an interesting discovery.

 

It's been done. It's usually encoded in the midrange though. Sounds quite strange.

A Google search using the words "spectrogram" and "face" brings up several hits, including:
http://twistedsifter.com/2013/01/hidden-images-embedded-into-songs-spectrographs/