To rule out the problem is the right channel monoblock plug the interconnect from the left channel of the preamp into the right channel input of the amp.
No hum/buzz the amp is ok.
You said you tried a different interconnect on the right channel, correct?
The loud hum/buzz/radio station could be caused by an open signal ground connection on the output side of the right channel of the preamp. An open ground at the input of an IC could cause the same problem. (The ground return could be broken on the outer shell of the IC plug at the preamp output end.)
No hum/buzz the amp is ok.
You said you tried a different interconnect on the right channel, correct?
The loud hum/buzz/radio station could be caused by an open signal ground connection on the output side of the right channel of the preamp. An open ground at the input of an IC could cause the same problem. (The ground return could be broken on the outer shell of the IC plug at the preamp output end.)