Eliminating Ground Loop Problem

OP a ground loop is the difference in voltage between two pieces of gear. A ground loop eliminator is BETWEEN the source and preamp/power amp. IF the noise is coming from just the Preamp, no matter the source or the power amp, that’s not a ground loop. BUT it could be a GAIN issue... from another source, don’t be fooled.

Another thing.. routers and Laptop power supplies. UNPLUG them.. Just for now... Noisy thing Especially cable company router box power supplies.. The older the box, the higher the noise level and power consumption.. My old cable box pulled 270 watts.. YUP.. I was floored, It actually required a ground loop eliminator via The Cable Company, Comcast..

Friggen ark welder... LOL

Regards

When I'm listening to music through 2-channel there's absolutely zero noise. When I watch a movie I turn my Marantz 7702 mkII, OPPO 203, and ATI  AT523NC 3-channel on to drive my center and rear speakers. The noise comes through my center channel speaker and rears. ATI told me to disconnect the interconnect cables from the amplifier and see if I hear a hum or any noise from the amplifier. I disconnected the interconnect cables and the amplifier was quiet. I have a wire going from the Marantz's ground to the ATI's ground. The wire reduced the noise, but didn't eliminate it. The noise can only be heard during quiet passages, but it drives me crazy.   

If you have the cable (tv) plugged in anywhere you need to isolate it. I have many I got for $8@.  Cable ground is NOT absolute/

FYI, the Marantz AV7702 is already lifted from ground, so you don't need any cheater plugs.  You can tell my looking at the IEC inlet on the back and seeing that there is NO ground prong.

You could try this:  disconnect all source devices from the Marantz (such as bluray player, satellite receiver, DVR, etc.).  Then see if there is ground loop humm at this point.  You can connect each source device (probably by an HDMI cable) one at a time to see if there is a source device that is creating ground loop humm. 

Another thing that can create ground loop hum is devices that are plugged into a different opposing-polarity circuit.  If you have identified a bad source device on the Marantz, try plugging it into the same outlet / power conditioner as the amplifers (same with the actual Marantz).

Sometimes ground loop can come from a cable box or a satellite receiver with improperly grounded dish/COAX wiring.  You may need to get a COAX isolation transformer - something like this:

https://www.amazon.com/Ground-Loop-Isolator-Transformer-Eliminator/dp/B08FRGH4X2

They are very easy to install inline with the coax cable that screws into the cable box or satellite receiver.  Be aware that these devices may not work on some cable boxes or satellite receivers.  Some receivers/boxes can't communicate with one of these isolation transofers on the line.  However, sometimes this can improve the image quality and the audio quality of the cable/satellite.

The noise comes through my center channel speaker and rears. ATI told me to disconnect the interconnect cables from the amplifier and see if I hear a hum or any noise from the amplifier.

Make sure the ATI amplifier and the stereo amplifier and preamp are plugged into the same AC circuit.  If they are plugged into opposing polarity circuits, this can cause ground loop as well.