To Float or not to Float...

Thanks for all of your responses.  Cleeds triggered the solution when he (or she) wrote "a properly grounded power cord", which reminded me that I was having intermittent problems with the connecting plug of the preamp's power cord.  Swapped out the power cord and problem solved.  I also have a pair of DeHavilland mono block amps with the same ground/float switches, and in the manual it states that leaving the switch in the "float" position may result in a "cleaner sound".  At any rate, a fully functioning grounded power cord has done the trick... 

Thanks, Jim.  I also use the preamp with a solid state amp that has no ground lifting switch, and keep the preamp switch in the "float" position.  Any danger in that?? 

Jim -
I have always used the preamp in the "float" position, whether it was with a solid state or tube (including the DeHavilland mono blocks) amp.  My impression was that sonically this was the preferred position, and as I mentioned the manual for the mono blocks even states a potential sonic improvement keeping the switches in the "float" position as long as there are no accompanying noises or buzzes (I can't seem to find the preamp manual to check, however it was planted in my head from somewhere (probably the manual) to keep that switch at "float").  Only recently did the buzzing begin which corresponded with some connectivity problems related to the preamp's power cord.  Now that I have switched to a different power cord, there is no more buzzing or noise, and all grounding switches are set at "float". 

Jim - My only front end source is a Resolution Audio Opus 21 cd player which uses a three prong power cord which presumably grounds it.  The cd player and preamp are both plugged into a power strip which I was told is recommended for use with Naim equipment and also utilizes a three prong cord and receptacles.  I initially thought the buzzing was caused by the interconnects between the pre and power amp, however swapping them out for different interconnects did not alleviate the problem.  I was have issues with the IEC female connector on the power cord making consistent contact, and, as I reported, changing that has seemingly solved the problem.  As to why the buzzing stopped when I switched to "ground" position, the technical answer is above my pay grade and I will let those of you with greater expertise ponder that...

I corresponded with Kara Chaffee, the designer of my preamp and mono blocks, and she concurred with Jim's post of 9/16/2017. The "float" switch only lifts the audio circuit from the cassis ground and the AC mains equipment ground remains connected to the chassis through the 3 wire grounding type power cord. Kara feels the units sound best with the audio circuits floated and that's the way I've always run them with no noise or buzz (except for aforementioned power cord malfunction).