UPDATE
Thank you to everyone who gave suggestions. I have booked my car in to my dealer next Monday for them to check if there is a problem. I will post the result here. Assuming that this is simply a 'feature' of Mitsubishi's ACC I will try reverting to standard cruise control although ACC...
I have had my new Outlander PHEV for about 10 weeks and overall I love it! However, the ACC beeps when a car in front comes into range and also when it goes out of range. This means that when following a car doing the same speed as me the car in front moves in and out of range constantly...