With this popularity there seem to be tons of ads before the podcasts even begin, every segment! If you're telling a story, that seems pretty immersion breaking. If you're just in the mood to hear interesting authors, well, that's what you'd like to hear, not what Joe Dentist can do for your smile.
I've found some interviews with authors, readings from and discussion of classic mysteries, and one old Radio show.
Classic Mysteries Podcast with Les Blatt
A vast collection (over 500) of readings from the works of some of the Masters and Mistresses of the Craft of Mystery Writing. Les then talks about the work itself with observations about the author.
I Love a Mystery is an American radio drama series that aired 1939–44, about three friends who ran a detective agency and traveled the world in search of adventure. Oldtime Radio show With Jack, Doc and Reggie (2016 most recent)
Interviews with Authors of Mystery, Thrillers and Suspense with Alan Petersen.
Interviews with authors of mystery novels, from thrillers to cozies and everything in between. Host: Laura Brennan
Speaking of Mysteries with Nancie Claire Interviews with Mystery Authors
An interview with Nancie on Jungle Red Writers that's pretty interesting: