Since updating to Android 9 (Pie) a few days ago, my Nokia 7.1 makes alert noises every 30 seconds - 1 minute until I view the notification.
I think it has something to do with the Ambient screen notification setting. I used to have it set at "periodically" which is supposed to be every 2 minutes and would previously just illuminate the screen - not make noise. But now, I get a notification noise about every 30 seconds (37 seconds to be exact) until I acknowledge the notification.
I set the Ambient screen notification setting to be "once" and that seems to have resolved the issue of getting the notification sounds, which is why I believe that setting is no longer working properly.
I can live with that workaround for now, but it really would be ideal to have my screen light up every 2 minutes without noise in the many cases that I don't see it the first time.
I have seen a similar issue reported with a solution of "Tap your Settings, scroll down and tap accessibility, scroll down and tap notification reminder." but I do not have that setting.