I have posted here numerous times since February, that it is quite common to have witnesses report more shots than were actually fired.
So hopefully, one last time.
A gunshot's sound pulse or wave pattern will reflect off objects. At greater distances when these reflections off other objects reach the listener, they will be far enough apart in time that he/she will be able to differentiate the reflections from the direct gunshot pulse. At close distances, such reflections will be too close in time, and the brain will incorporate them as one pulse (shot.)
At greater distances, the reflections may bounce off other houses etc, and these reflections may be heard as separate gunshots. The reflections are commonly called echoes.
All Pros. needs, as I have said, is a physicist witness to explain this.
And IMO, the key point RE PM charge is the 17-minute gap between the 2 sets of shots. THis, of course does not change regarding echoes heard during either set of shots.