If you want to have a listen to the Pip yourself, as well as many others like the squeaky wheel and the buzzer, check out this WebSDR implementation:

http://websdr.ewi.utwente.nl:8901/

and for a much wider list of frequencies of number stations, and radio anomalies you can take a look at:

http://priyom.org

they have times they broadcast figured out there. if you enjoy this kind of stuff, i suggest picking up an SDR yourself, i know i do. my $20 RTL-SDR works well for playing around with this.