This is my first post and just picked up my 328i Sport 10 days ago. I am having this same exact problem. I put my car into reverse and I get the constant tone and red bar that something is right in front of me, but there is nothing. The display is showing the right center sensor in full red. I have cleaned the sensor a few times and even used a clay bar thinking there was some contaminants on it, but it still happens. There have been a few times that it works perfectly normal, but for the most part, I get the constant tone.
I'll give it a few more weeks, then I'll have to bring it in.