1997 BMW 740 User Comment / Complaint

Hi, i am not sure if this is a safety defect or not. i had a sound like an expanding and contracting of metal in the back underneath of car. it sounded like a cookie sheet when it is first heating up in the oven and it expands and contracts. the dealer couldn't find anything when i brought it in but said that they were going to call bmw technical support because they had a theory that a spider was clogging up the fuel line and that this had happened once before to their knowledge and resulted in the gas tank collapsing. i brought car in again and they said they removed a spider and put in a new pipe/line. the sound i had heard before was gone. some people have told me, however, that the whole system is a closed system and that this couldn't have happened. is it possible? is problem fixed?