I had this start happening. Turned off the NFC sound setting. Annoying though because I use my phone for payment regularly. Found the issue. I have a cover on my phone that has a compartment to store two to three credit cards/ drivers license on the back. I was storing a credit card back there that has the NFC chip on it. The phone picks it up causing the notification sound to go off every time I unlocked it. It also screws with the phones ability to use NFC when using it for payment. I can't store it there. So... If you have something like this, take out the credit card that has that feature and it will go away.
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