Well, I don't know how to check for "strange" things in general but I don't have anything weird or customized about my phone. What I observed (which led me to conclude the use of the alarm API but I don't really know that's how it's happening):
I am running Android 8.0.0. PvZ:H would make a sound every time I got a notification from it. This continued even if I turned notification sounds off for PvZ:H in the "app permissions / notifications / allow sound" for PvZ:H.
Then I tried turning off notification permissions entirely for PvZ:H from the app permissions setting. I didn't get the notifications any more but the sound still happened whenever I would have gotten a notification (whenever my event boost refreshed, or at 7am).
Also I should note that the sound occurred even when I had my "media" sounds turned off and only had "alarm" sounds turned on. It also happened when I had the phone set to "priority only" which only lets through alarm sounds and designated apps. These are what led me to believe that PvZ:H was using the alarm API.
Finally I turned off notifications from within the app and then the sound finally stopped.
