Ohhhhhh you have two wireless transmitters going!\n\nIf the subs have them built in, why would use an external one?\nThe Klipsch are wireless built in recievers but come with a transmitter you plug into the reciever. The polk are not built in i bought the Sunfire wireless transmitter\/reciever to use with them and when I use the Sunfire to the Polk it hums. \nBut when I disconnect it and use Klipsch either one or 2 subs and 2 transmitters no hum.\nThe polks are better speakers all around that is why I upgraded. One Klipsch is ok and 2 is good but one Polk is superior to 2 Klipsch and 2 Polks running is closer to theatrical sound of full enveloping 360 degree sound. Which is why I am pushing to go with the Polks. \nI ordered the Audioengine wireless sub transmitter yest it will be here Wednesday to compare and see if it is just the Sunfire.\nI had ordered a ground loop isolator but delivery got postponed.