Best answer by Wilfried
I had also reset my cell phone at the same time. And the beep was effectively gone.
But since this morning it was back. Together with my son I looked at everything and listened to it.
And yes, effectively, the beep came from my cell phone . It was a crappy app (something i installed a time ago) I removed it and the beep is now gone. So no beep from my watch, no speaker in my phone .
Thank you SDSI and Ove for making me doubt and researching again.