Although the manual suggests connecting both the speaker level and line level feed at the same time, I find there is a quiet hum from the speaker when both are connected. This immediately disappears if one or the other lead is disconnected. Does anyone know what this is and if I should be concerned? My dealer did mention to me that he does not generally connect both feeds as he has the same problem in general with REL speakers. I am using a Denon 2801 amp, B&W 602 main speakers. It is a brand new Stampede, using the supplied connects. Thanks for any comments.