Strange Morse Code-Like Sounds on phone Line

Just recently, i was calling a business colleague on the West Coast (USA)-througout the call, i could hear a faint clicking-sounded like morse code. Anyone know what this is?

Possibly a mobile phone interfering with the equipment at one end or the other - cellphone transmissions are able to do this to all sorts of equipment that has an audio amplifier in it. It makes a sort of dit-di-dit, dit-di-dit, dit-di-dit, brrrrrrr sound