I have a 400-CX I am working on that has an annoying hum in both channels, although louder in the rt. channel, this is coming from the AUX position. The strange thing is that with aux 1 shorted and the chosen input I get the hum, but if I chose aux 2, the hum goes away even though that channel input is not shorted. Also, if I choose the phono input, no hum there either. I can see the hum on pins 3 and 6 of both V7 & V8 (1 mv) and pins 3 & 6 of V6 & 5. It is also present at pin 6 of V4 & 3, but much reduce. The PS has been rebuilt by another respected tech, who basically rebuilt the whole thing. Any suggestions? Thanks!