My MKI's don't hiss, but they do exhibit some popping or clicking for the first few minutes that they're on. I had chalked it up to perhaps thermal expansion of the heat sinks rubbing against the plastic case, but in truth the amplifiers probably need servicing.
The displays are more curious, especially since both failed at once. Assuming you're not daisy-chaining, try switching the two SpeakerLink cables at the back of the 9500? (so that left and right are temporarily reversed.) Ridax is the real expert on these displays.