Ok, so I found this;
Hopefully, this is a grounding issue, as Al suspects, and one of his recommendations will solve the problem.
I do have a couple of additional thoughts. First, I noticed you used only three of the four wires in the Belden speaker cable, which would result in an unbalanced configuration with one polarity having a larger gauge wire than the other (whichever side has two wires vs. one). Since most speaker cables use the same gauge wires for the positive and negative poles, you could try connecting the cable in a star-quad configuration where the two wires opposite each other are connected together to form each polarity. Based on the pictures I found, it appears you would connect the black/white wires together and red/green wires together.
Also, you might check the polarity of your wire connections in both channels to make sure they are consistent.
REL manages the lower frequencies differently than other manufacturersÂand does so with excellent result. While the company offers line-level RCA inputs, these should be used only as a last resort. The supplied Neutrik speakON connector utilizes a high-level connection that goes directly to your power amplifierÂs speaker outputs. The subÂs high impedance does not affect loading of the main speakers, thus allowing the character of your amplifierÂs sound to carry forward into the subwoofer.My first thought was to recommend trying the line level outputs from the preamp but it appears that using the high level speaker cables to connect the sub to the speaker cable output terminals of the McCormack amp is the preferred approach, since that is designed to result in superior blending with the sound of the amplifier that is being used to power the upper frequencies.
Hopefully, this is a grounding issue, as Al suspects, and one of his recommendations will solve the problem.
I do have a couple of additional thoughts. First, I noticed you used only three of the four wires in the Belden speaker cable, which would result in an unbalanced configuration with one polarity having a larger gauge wire than the other (whichever side has two wires vs. one). Since most speaker cables use the same gauge wires for the positive and negative poles, you could try connecting the cable in a star-quad configuration where the two wires opposite each other are connected together to form each polarity. Based on the pictures I found, it appears you would connect the black/white wires together and red/green wires together.
Also, you might check the polarity of your wire connections in both channels to make sure they are consistent.