Reverse sensors will beep with bike rack and bikes
I know the reverse sensors system will beep (not continuously) when you have a bike rack with a bike on it. According to the manual "a control in the message center allows this to be disabled", but I think that's wrong. I just went through all the menus and can't find a way to disable it. Not that I care to disable it anyway, I just checked before posting.
My friend's Explorer allows you to disable the rear sensors. I think because it has a towing capacity and makes sense if you want to back a boat into the water without the distraction of the warning beeps.
Since the 2012 Focus is not rated for towing it makes some sense that they don't provide a way to disable the rear sensors.