I actually had a problem like this with my Marantz receiver, I had to send it in for repairs, thankfully under warranty. But the DSP board was cracked, and they tried to re-solder it, but that didnt fix it either, so they had to actually replace the whole DSP board. Since then I havent had a problem, you might actually have a defective unit that needs repairs. But the exact same problem happened to me, only on signal via Digital Coax or Fiberoptic.