Experience with Inline Ground Loop Eliminators?

@bluethinker So if I'm understanding your question and explanation correctly your preamp and monoblocks are plugged into two different outlets on two different circuit breakers?

bluethinker 

the LTA preamp and AGD monoblocks both connected to a Puritan 156, so they are both on the same AC line ... I disconnected the RCA cables between the LTA and AGD units, the hum went away through the speakers. According to ChatGPT, it’s probably a ground loop issue between those components. 

If the amp and preamp are on the same line, then the origin of the ground loop is elsewhere - such as a source component connected to another AC line or ground. The preamp then sees the source ground potential through the interconnect. To troubleshoot, you can disconnect your sources one at a time to test if the hum goes away.

ChatGPT's advice is only true IF you have no upstream components also attached.  For instance, one notorious source of ground loops is cable TV boxes.  Even if turned off, if you had the cable TV box attached to your preamp and amp you'd get a ground loop.  

So, that's why I'm asking. 

PS - That same loop also can happen from anything with an external antenna, like Satellite TV, FM, etc. 

Also, a connected PC will do this too, so before diagnosing this as a striclty preamp/amp problem make sure you've physically pulled off all upstream devices.