Due to the loss of powerful radio broadcasting and the take up of
digital technology, and other broadcasting that does not leak into
space the Earth is gradually getting more and more quiet.

"According to New Scientist our transition from radio transmissions to
cable TV could mean that our window of detectability is no more than
100 years."

http://www.theregister.co.uk/2004/08/10/alien_hunt_wrong_freq/

I wonder if this is why if there is intelligent life out there we
cannot trace it. Maybe they all have a phase of going from noisy radio
transmissions to gradually getting more and more efficient transmission
technology and disappearing from view.