Distortion from speakers - amp?

Friends, I have a new amp (Halcro MC20) and preamp (Atma sphere R13) that I have mated to my beloved Newform Research speakers. My previous set up was a Pass Aleph 5 and Blue Circle 21 preamp. While the new configuration sounds wonderful, I am hearing very audible distortion, greater with one channel. With the ribbons, it is a buzzing sound, and in the bass drivers like a feedback hum. Again, when I change the channel cable connections between the pre and amp, the sound changes sides as well. It does not seem to be dependent on volume setting. Turning it up does not increase the distortion. The preamp is stone quite but the amp has a bit of a buzz when it is on. Ideas? Thanks much.