I listened to the discourse. Let me summarize.
1. There are many things in this world that average humans cannot perceive. There are unseen beings living among us (gandhbbas and some petas) that we cannot see, but those with iddhi powers can see.
2. @29 minutes, the Thero discusses the following account:
“The Siberian Hell Sounds”
– The Thero says he has heard similar “hellish sounds,” while being in samadhi a couple of times, but he did not want to hear them again.
3. @35 minutes, reference is made to the following video (I believe):
– There is a book, “23 Minutes In Hell: One Man’s Story About What He Saw, Heard, and Felt in that Place of Torment” by that person, Bill Wiese.
4. I have discussed some of these in the post “Does the Hell (Niraya) Exist?”
– I need to include Waharaka Thero’s experience (in #2 above) in #4 of that post. I was skeptical about that sound record when I wrote that post.
5. Many suttas describe the propensity to be born in an apaya. There is a series of about 30 suttas starting with the “Manussacutiniraya Sutta (SN 56.102).”
– According to those suttas, most of those at the end of their human or Deva bhava are reborn in an apaya.