I'm thinking the problem I had here could be a common occurrence with many so I wanted to provide some more info here in case it might help someone.
I was picking up a low level buzz/hum on my phono despite the fact that everything appeared grounded properly. I only noticed it recently after moving a larger pair of full range speakers into a relatively small listening room.
The problem was the pre-amp was sitting directly on top of a new/different amp that I had put in the system a few months back and the proximity of the amp was producing some sort of inductance issue with the phono section in the preamp that caused the noticeable low level hum/buzz at higher volume settings.
I only noticed the problem when music was not playing and the volume was up, but I suspect it negatively impacted the sound quality when playing as well when occurring even though it was not directly audible because I thought I had noticed a difference in the sound of the phono since replacing the amp, which improved the sound overall in most in every other way.
The solution was to separate the amp from pre-amp by 15" or so.
Just something to keep in mind perhaps should a similar problem ever arise. I suspect it could happen with almost any amp/phono preamp closely located together except perhaps with very top line preamps with exceptional casing build.
In the case of my Carver pre-amp with built in phono section, its built like a very sturdy jeep perhaps but not like a tank as are some higher end pieces.
