So, I searched this forum and found some postings on the speaker hum. But, I still can't figure it out? I had this at two different homes? Ruled out electrical grounding? Disconnected everything except for speakers and DVD player. Used 3 diff optical cords....tried 2 diff DVD players...changed out speaker wire. THis hum starts after receiver has been on for a few minutes. Any ideas?
Grounding issues that are external to the receiver will in almost all cases be there as soon as you power up the unit or the one component that is causing the problem is placed in line. If the unit is quiet at start up and after a few minutes of operation shows noise, then it's possible there is a bad connection or failing component within the receiver that is causing the noise.
You state you've had this receiver at two different locations but did not say when the noise first showed up.
Strip the unit down to nothing more than the receiver and speakers. Using the tuner for a source either the noise appears or it does not. If it shows up, the problem is in the receiver or the incoming AC line. You could be picking up noise from another component or appliance plugged into your AC panel.
If the noise is not present with just the tuner, then switch through the input selections to see if any other input causes noise when nothing is plugged in. If there is noise in any of these situations and you rule out noise from another component somewhere else in the house, have the unit serviced.
Unless you know the headphones are driven from the speaker outputs using headphones will only prove that the headphones operate as they are designed. It's rare to have headphones use the speaker outputs in a modern receiver, there is typically a small op amp designated just for high impedance headphones and this comes into the circuit just after the input selector switch. Unless the problem occurred in a component well within the intial input stage of the pre amp section - as in before the selector switch (or in the volume control) where there isn't much circuitry - your solution might not show any noise though the problem could still exist within the receiver.