Welcome to Android Central! Although this may be due to something on the phone, keep in mind that it might also be due to your car's system. I recall renting a Nissan Altima that had an auto-response system when somebody texted me -- I had to go into the car stereo's menu to turn that off, not the phone. So let us know which car (make, model, model year) you have, and if it has the factory-installed stereo system or an aftermarket one.