Reddit reviews Legion (Original Television Series Soundtrack)

It's an electronic beat that starts at around 27:00 in the episode and sounds sort of like a ticking clock/alarm. Immediately that song is when the machine is turned on that David is attached to (to remove the parasite) and the Pink Floyd song "Breathe" begins.

Here is the scene

I'm guessing the 30 seconds of song that you're looking for is original score. The original score is by Jeff Russo and can be sampled or purchased here. Though the sample doesn't seem to show the section of music you're looking for