I remember being in grammar school listening to EG Marshall's Mystery Theater. It was a bit hard to grasp when I was a kid, but now I started listening to it on youtube. I highly recommend it if anyone is into spooky suspense.
I am a massive fan of OTR (old time radio). I listen to it streaming constantly, and the Radio Classics channel on SiriusXM is one of the presets in my car. The Great Gildersleeve, Gunsmoke, Dragnet, Jack Benny, you name it.
I like Broadway Is My Beat, but my favorite mystery drama/whodunit is Yours Truly, Johnny Dollar, no matter who was voicing the role of Johnny Dollar. I could easily see that show -- in which an insurance investigator tracks down the persons behind fraudulent claims -- getting remade for a television audience today.