Random notification tones during phone calls with no actual notifications

Randomly my phone is making notification type tones during my calls. Not every phone call and not at any regular interval. The tone can play twice in 5 seconds and then again 20 seconds later in the same call. This happens throughout the duration of that call but may not happen during the next call. There are no actual notifications, no emails, no texts, no other app notifications visible at all during or after the phone call. I don't want to turn off and miss actual notifications during my calls, but how can I make this random notification of nothing stop??

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