The start of an arms race?
Not sure - I don't speak Dalek.
Any caller ID?
London number calling one of our London numbers...
Is it dial up?
Sounds rather like a pearl/blue box configured to walk through all possible DTMF frequency ranges, looking for something exploitable.
Sounds like a blue/pearl box, potentially, configured to walk through all possible DTMF combos to scan for vulnerabilities in PSTN systems...
When the tone stops, it means the nukes have gone off.
It's what my kids call music !!
I got something that sounds like that once when I'd messed up the config on an isdn trunk. Too long ago to remember the specifics but I do remember the sound
I think that's called dubstep.