It is most likely a ground loop. Basically there is an unwanted potential difference between Lyr 2 and the rest of the setup. There are several ways to break up ground loop and some might or might not work for you. Sometime as simple as using a different power socket is enough to eliminate the problem, while other time you might need a ground loop isolator somewhere in the setup, such as iUSB.
12/15/14 at 1:29am