Originally posted by coldkidc
There's no way this can count - any number of sounds could have been made simply by the movement of his car or the wind, etc.
Although it is possible this may be another of the weird worldwide sounds, I have to agree with you strongly here.
Panel vibration, exhaust vibration, worn bearings on engine pulleys, driveshaft vibration, worn window seals, grill vibration or dashboard vibration
are just some of the reasons that could have possibly been the source of this noise.
He should have stopped his car and turned the engine off to get a better, more credible audio sample.
Good to have a record of this noise anyway in case more instances of it happen in the future though.