I should add that the hum happens not just with the Tivoli's "mix in" but with the "aux" input as well. Also, here's how the sub is connected to the tivoli: a 3.5 mm (1/8”) male-female TRS/jack plug goes from the Tivoli's Sub Out, and then mates with a male 3.5 mm (1/8”) TRS/jack plug, which is yellow and black RCA on its other end. These RCAs then go into the sub's RL inputs. Yellow is left, Black is right.