Samsung Galaxy S3 — car mode enabling issue

My S3 keeps switching on car mode by itself and then switching it off again a fraction of a second latter. on, off, on, off, on, off it's driving me nuts! I never selected the car mode in the first place (and don't know how to anyway!) It's making using the phone difficult at best and now I've had to switch the sound off on my device as it's constantly bleeping on and off! I need help please!