Low level noise from spkr when nothing is playing

It does not change my overall listening experience and I appreciate your input. As you all know, it is easy to be overly focused on every little thing. At the end of the day, I love the sound.

Grimace, I do not know what you mean by ground loop, lots of threads? How did you fix it in your system?

I had the similar issue with my AV receiver, except that it suddenly developed in my LF speaker.I ignored it for a while, but within a short time more audio problems developed.

I ended upn shipping it back to the distributor for a warrnty repair - some of the circuits had been fried and new parts and circuit boards inserted as replacements.
Speculation is that a sudden power surge (repeated) caused the problems.

FWIW ....

It could be a ground loop issue, meaning that you may have a "dirty ground" feeding noise thru the amp. Have you tried a cheater plug to lift the ground and see if the noise vanishes? To be clear if your amp has a 3 prong plug, try one of those cheater plugs that a 3 prong plugs into but only 2 prongs plug into the wall socket available at most hardware stores and usually gray in color. About buck fifty. Another path of investigation is try disconnecting the center IC between the pre/pro and the amp. If the noise is still there then you know it is coming from the amp. If it goes away then start tracing it backward thru the pre/pro and source components. Do you have anything plugged into the 6 channel pass thru on the Krell. Pull the center IC on that
and see what results you have. Once you determine which component is generating the noise, try the cheater plug on that and see what comes of it. I have had similar issues and it can drive you nuts. I chose not to leave it as I figured something is causing it. It could be as simple as a speaker cable crossing an IC or Power Cord etc. Good Luck.