不能直接让声音重复.
您必须发送另一个通知以再次触发声音.

You can't directly make the sound repeating.
You have to send another notification to trigger sound another time.

看看这个问题，它和你的很相似:
苹果推送通知，定期发出嗡嗡声

Take a look at this question, that is very similar to yours :
apple push notification with sound buzzing at regular interval