REL Sub Hum

@vinylshadow by cheaper plug, do you mean power cable? 

Thank you ALL!! I have a feeling its THIS amp (A23) and maybe it has developed any issue with grounding... my other parasound (2125 v2) with exact same configuration (ground to back amp terminal and yellow/red twisted to positive amp terminal). The A23 was working fine in the past with same RELs; I had put on the shelf for a month or two trying another amp and them plugging it in, identical as before and the issue started... which leads me to believe there is something going on in the AMP... 

also @sizzitrail84 I am running in stereo mode.... 

I am going to try the RCA method, @lak which the article you posted called suggested. 

Schematics are not easily available for your Parasound amps so I can’t confirm, but I wonder if the A23 is a fully balanced design and the 2125 v2 is not.   This would explain the different results when connecting the amps the same way.

Try connecting the A23 as differential/fully balanced per the REL manual (page 15 in my Serie T/x Operating Instructions).  That’s Yellow to the Left + terminal, Red to Right + terminal, and Black unconnected or connected to ground.  This is how I connect my differential/fully balanced amps to my REL T7/x without any hum.

@mullster No. A cheater plug. It goes on the end of the subs power cable and into the outlet. It eliminates the ground prong

@mullster I have not had any issues when connecting my REL subs with the speakon cable however I did have a hum issue with a different brand of sub that connected with the speakon cable. Adding an RCA interconnect and following the directions provided in the above video I posted worked for me.