That's the next step, just have some other projects to get out of the way first. There's a fairly low cost infrasound recording option using loudspeakers[1] that I think is worth a try. I'm also interested in building a seismograph, which might be able to pick it up on the high end of its range. If the sound is anywhere as loud as I hear it, there isn't much need for anything ultra-sensitive.

[1] https://www.youtube.com/watch?v=mekmsgjSqR4

I actually plan on recording sounds from my head, too. Could be weird spasms or something causing it, the lack of any variation in the two pitches makes that seem unlikely but possible.