I have discovered that when My Macbook Pro (Early 2011, Mountain Lion 10.8.5) has an active ethernet connection, there is audible audio static/interference via the headphone socket.
The ethernet connection comes via a router which in turn is connected to ethernet via powerline. The audio interference is not there when I connect to the network via WIFI.
I would rather have an ethernet connection so am wondering if there is anything I can do to prevent this interference?
Switching off the powerline adapter at the wall instantly stops the static / interference so I'm pretty sure it is related to that.