Power adaptor causes buzzing on phone

I discovered yesterday that when my Mac Book is plugged in and
near the telephone at work, people on the call hear a buzzing noise.
If I move the laptop away from the telephone, the buzzing goes
away. If I touch the laptop while it is away from the telephone,
the buzzing returns. Last, if I unplug the laptop and run on
battery there is no buzzing in any circumstance.

Any guesses on whether this is a problem with my power brick or
my laptop or...is this expected behavior?



Mac Book Pro 1.83 GHz