Thanks Pent. The volume change at shutdown didn't work either. I
guess the phone is just running that shut down music too quickly!
Your note gave me an idea, though -- using Tasker to turn System
Volume (which controls the shutdown and startup sounds) down to 0
after exiting the Google Maps and Nav apps. Those apps always
maximize the System Volume, with Tasker I can let them do that and
then automatically turn that volume back down to 0.