A poor speaker connection wouldn't reveal itself as a high-pitched hum, so I highly doubt the banana plugs are to blame. What I'd do in this case is disconnect components from your amp/receiver one at a time (turning off the amp/receiver first, of course) until you find the one that is causing the hum.

But before you even do that, I should ask if the hum is audible at all volume levels and with each input selected.