If it only chimes when getting out of zero volume, then I would try to set the volume to last used in the menu and before putting it in standby just lower it to 1. If my memory serves, it’s possible thru the set up menu.
Secondly, the Ref 6 has 15db of gain and you’re not only mismatching impedance with the Hegel amp but also, due to the high gain of the amp you’re limiting the usable volume range. It must be pretty narrow and each step increases or decreases the volume by a lot. Not a good setup.
If you like the Ref 6, and it is a very nice preamp, you should probably match it with either an ARC amp or a solid state amp that presents a proper load and has less gain.
Few other things that come to mind - make sure the Ref 6 has plenty of space around it. Place it on the top shelf if you haven’t yet with nothing above it. Allow it breathe. Are you using the rubber tube rings? If not, you should. Is it plugged into a power conditioner? Try it with the conditioner and direct to wall and see if any change in noise.
And call ARC to get their take on it.