I have an, albeit old MX-136 connected to an MC207 amp. The components(DVD, Apple TV 2, Sony TV connect to the MX-136 optically and I have used XLR, RCA and the RS232 to connect the amp and preamp. The only other connection is the remote cord. The noise problem seems to be a 60Hz hum. At volume 0 there is nothing, at 1 or more the hum is there, but it cannot be amplified. I have tried the following: isolating just the amp and preamp on 1 circuit, removing the cable tv at the home input, removing the grounding pins on the AC cords, removing all inputs. I took the unit to the dealer, and the noise was present. I took the unit to a buddy's house, still there. I brought in several test units and hooked them up to the amp...NO NOISE. I had the unit sent to an authorized McIntosh repair depot, and they did some wizardry which reduced but did not eliminate the noise. I then contacted McIntosh who sent me a unit that was in their demo room. Upon hooking that unit up, the noise was still there. Since I used other preamps with no noise, i have to assume it is in the preamp and not the amp. Is there anyone out there who can offer up a suggestion on how to fix this.