I have a UPA 500 along with a UMC 200. I bought both at the same time two years ago. On Sunday, I heard a pop in my right surround sound speaker, followed by crackling. I changed speakers and still heard crackling, so I know it's not the speaker. I unplugged the right surround from the UPA and the 200, still crackling. So it appears that it is an amplifier issue Has anyone had this problem before? Suggestions?