Hello Al, Ralph, all,
I disconnected the inputs on my stereo dual module Class D amp last night, and the right channel was silent. Inexplicably, the left channel was still noisy. Today, I rounded up some spare I/C's that were long enough to reach between the preamp/processor and the amp, disconnected the leads from the pre-pro to the separate tube preamp, and connected the amp directly to the pre-pro. The two channel and three channel Class D Audio amps are now quiet as a tomb.
From here on out, all my HT and multi-channel listening will be through the Class D amps, and two channel listening will be through the SET 300B and Transcedent Sound Grounded Grid preamp.
So your idea of the problem being input-related was spot-on. I also found I had my surround speakers connected to the rear surrounds on the pre-pro, which may have been causing some of the problems as well.
So, everything is working much better now, though I will be limited in my use of the Class D amp. I will have to re-think my connections to see how I can better utilize the Class D stereo amp, but at least for now, mission accomplished in attaining blessedly silent noise-free listening.
For that, I can't thank you men enough. Having your input on this forum is a true blessing!
Regards,
Dan