If your audio and power cables must intersect (as they do for most of us with real world setups), do your best to make sure they intersect perpedicular to each other (90 degrees offset). Any EM interference would be at the minimum that way.
In my experience, however, the Coax cable is the culprit 90 percent of the time. What gonk says is true - isolators for coax are cheap and effective - however if you don't have a power line conditioner (here comes my sermon
), I suggest you get at least a basic one to make sure your new 755 is around for a while.