I emailed Robert Scherer (who is “rps” of the above site) to draw his attention to the thread and as an owner he said:

“A couple of folks on the thread were wondering why pusher turboprops like the Starship make their signature “buzzing” sound. The sound is caused by the turbine exhaust passing through the propeller disk.

All the best,

Robert Scherer
Starship NC-51 (N514RS)”