Respuesta :

Dezbooboo123
Not long after we left I began to notice a knocking sound in my car [tex]Before[/tex] there had only been the purr of the motor....... So the word you're missing is before which makes sense in the sentence... hope it helps :-)
ari1471
Not long after we left I began to notice a knocking sound in my car. Before, there had only been the purr of the motor.