For sure, grounding the REL to another piece of gear or a line conditioner usually clears up the hum. If you’re dealing with Class D amps, extend the ground wire if needed, but keep it short to avoid any new issues.
James,
I tried to use the rca cables for grounding to both mono blocks. I’m still getting the nasty buzz. I guess I will try to contact REL . This is not fun, but hopefully this issue will get resolved.