For this 29c3 CTF challenge, we are given a WAV. Upon first listening, one can hear DTMF tones, phone tones. There is still an abundance of high pitched noise too. First check with Audacity in the spectrogram:
This challenge gave the description: Ever played Googlewhack? Well, this is a bit easier and gives you more power, enjoy. Googlewhack is when only one result comes up from two words being searched. In this case, they have their own database of strings and we can search to find something that returns only one result.