This one is just plain old strange.
This one is just downright strange, but we're there's a logical explanation for what's going on here. Just caught testing on the Nurburgring, a pair of Mercedes-Benz CLAs each happened to make the same weird whistling noise as they passed the car spotter's camera. Strange we know, but we do have a few possible explanations. First up, it's possible that there are some improperly fitted body panels, something not unusual to find on test mules.
Another explanation could be the exhaust or some other engine component(s). What also can't be ruled out is the fact that this video was filmed from only one section of the track; are weather/wind conditions to blame? Anyway, everyone is welcome to chime in with their own theories.