First, let's get one thing straight. YLVIS' idea of fox noises is more like a person having a stroke. Example: JaJaJaJaJaKaKaKakaKAkAKAKAkacall_an_ambulance. I can safely say that this is NOT the sound that a fox makes. It is kind of hard to name it because they can make so many different noises. Sometimes it sounds like coughing, other times it's auto tuned high pitch screaming. Often it is a combination of both. If you want some examples, check out these links of 4 different foxes making different sounds: