dual monitor making noise

I want to use a second monitor, i have attached the adapter becuase my monitor doesnt have DVI when i plug it in, all i can hear is this buzzing sound,

how can this sound occur? i have figured out that the monitor is somehow outputing this sound and its going into the macbook through the monitor cable.

this is just really weird, how is this sound coming into the macbook through the monitor cable??

thanks