I hate to beat a dead drum

Heard on a talk radio sports show. A caller was apologizing to Ron Cook for raising the same issue as all the other callers. This is a conflation of “beat a dead horse” (to continue to focus on something) and “drum into (one)” (teach someone something through intense and frequent repetition). Both idioms refer to something continuous or repetitive. Also, the word “beat” is connected to “drum”. “Beat the drum” (promote or support something or someone) might also be in the mix. Kudos to John Kooser for hearing this one and sending it in!