Hello @Js4 and welcome to the community!
It might be hard to figure out what is this sound exactly, it would help if you record a video of it and post the link here. But one of the most common sounds that gets people confused is the NFC read error sound, and will happen if your phone's NFC tag touches other NFC tag containing gadgets, like other phones, tap-to-pay credit cards, and many other gadgets.
Do you have a credit card or transportation card fixed into your phone case?
