I usually activate Waze while I'm still at bedroom (morning) or in the office (at EOD) so I can use the WIFI and review the route before getting in the car.
In both cases, I don't want to wake up my souse and kids in the morning nor notify the whole office that I'm leaving soon, but the starting navigation notice sound "Route is ready, let's get started" does just that !!
There's really no need for that so it should be totally removed or at least allow the user to disable it permanently, without the need to silence the sound for every trip and re-enabling it in the car.