I noticed this too. I’m assuming that the resting position for the baffles in the exhaust are normally open (loud mode). When we start up cold the Engine Control will richen the mixture and increase RPM for quicker start and warm up. (Engine has to be in Closed Loop fuel control within 90 sec per law). I think the rich mixture start with baffles open (they close in a couple seconds), causes the pop/explosion which does a great job a rattling my neighbors windows. (Heh, heh...)
BTW- what part of San Diego? My brother is in Ocean Beach...