My car die'ed om me the other day. I was lucky I wasn't on the freeway. When My service person looked at my car to get it restarted I asked him about the air pump noise. As it turned out I don't have a air pump on my car. (Maybe because it's 118 years old). We did find out the battery went bad and that is why my car die'ed. He put a new voltage reulator in the alternator (just a precaution) and replaced the battery. He said the alternator was having to put out so much electricity to keep the batery up that the alternator was making the noise. Hopfully problem solved.