The song "The fox" about the sounds that animals make is taking the internet by storm. The chorus goes: "What does the fox say?". Interesting question! Two articles, one in Wired.com and the other on Popular Science answer the question.
According to Wired one of the suggestions made in the song, namely "“Chacha-chacha-chacha-chow” comes pretty close.
Popular Science says the fox most often does a series of barks like "ow-wow-wow-wow", but very high-pitched. There is also gekkering a guttural chattering with occasional yelps and howls, like an "ack-ack-ack-ackawoooo-ack-ack-ack". This sound is made when they communicate with foxes in closer proximity.
And here is the music video:
'via Blog this'