Two days ago I was driving my 2013 Megane RS and I heard a rather strange, rattling sound when accelerating. Since it also sounded scary and I was close to the garage, I went there immediately. After inspection, it appeared that 1 spark plug had come loose and damaged the thread in the head. So now, at least, the head off or more, etc. My question now is, is this something that according to the dealer can happen spontaneously or did they just not tighten this spark plug properly at the last turn? Or any other reason? And if so, how do I prove that?? Btw, the car runs on LPG. And also the mileage is 98000km.