I have an analog receiver connected to a laptop via an RCA to 3.5mm jack adapter then a 15 or so ft 3.5mm cord running to the laptop. The speakers that are connected to the receiver, when on the laptop's input, play FM radio.. even when the FM antenna is pulled from the receiver. Recently, I ran a CAT 6 Ethernet cable to the laptop and now the FM radio volume has increased, and a loud buzzing sound has started coming from the speakers that are connected to the receiver. As soon as the Ethernet cable is unplugged, the humming stops. How can I fix this?