Hello,
I'm French and I still don't have an answer.
I have noticed a little noise when I receive a call on the iPhone when it is in vibrate mode and "lift to activate" is disabled.
The iPhone vibrates well but there is a little sound coming out of the speakers (a little short noise) with the vibration "synchronized".
When I put another vibration "accent" or "pulsations" 'in settings) the little "little short noise" disappears.
The sound I hear seems to come out of the speakers because when I approach the iPhone, the little "little short noise" comes out of the speaker from the bottom and the top (notch).
Here are links to videos that I recorded and put on Youtube to listen to the mysterious "petit bruit court":
No bug (test in settings) : https://www.youtube.com/watch?v=6kET3aj8juE&feature=youtu.be
With bug (Incoming call in vibrate) : https://www.youtube.com/watch?v=PlhgHVRXKjU&feature=youtu.be
I forced the reboot, restored the iPhone (tested without putting back the backup) and still the same problem.
I think it's the hardware bug because when I test the vibrate in the settings/sounds and vibrations/ringtones/vibration/synchronized, there's no "little short noise".
But when a person calls me on the iPhone and the iPhone is in vibrate mode, there are these little short noises.
You'd have to do a test on another iPhone 11 to see if they all have the same problem (but there should be no noise around where to listen this bug).
I'm under iOS 13.3.1 on my iPhone 11
Thanks for your answers because I think it's a software bug.