One of my red and black for my speeker isn't working. The top one works fine, and so do the speekers, it's just the bottom right and left input for the speeker that won't work, and when i do have the power on with both speekers plugged in i get a humming noise. And before if i had one speeker unplugged and another plugged in it would still work if it was on, but now since i was trying to find out what the problem is, if one speeker isn't plugged in the receiver shuts off. any help? is it possible to replace the right and lefts? thank you