I don't have a Note but my Xperia X rarely makes a sound when I get a call, if I'm lucky it will vibrate once and sometimes the screen remembers to light up - I can have it in my hand waiting for a call and still miss it which is not ideal. Sometimes the touch accuracy seems to be off too...

No interest in android apps so I will add the note 4 to the list of options. Finding a good unlocked one may be a bit of a challenge though.