Right now, the two episodes of TWiG that are in Megaphone (the platform TWiT uses that does this) are NOT tagged for ads. (However, this week’s will be.) We tested with Triangulation and Valley of Genius, so you may have heard a dynamically inserted ad if you were listening to either of those retired shows.
…or was this happening in Pocket Casts with a non-TWiT show? If it’s not TWiT, then I don’t know what may be inserting the ad. If you can point me to the show, I can probably figure out what’s being used to insert the ads dynamically.