Seventh Circle Audio

I have a rack with 2 N72's and 2 A12's. The light pulses and the sound fades in and out with the pulsing. It was not doing this for a while and now it is. I have tried it with the phantom off and on with the same result. I have read on other post to try disconnecting some of the units. The power supply was built by Seventh Circle. All of the other units I built myself. Any suggestions?

thanks

Disconnect all the modules from the supply. If the symptom disappears, then...

Connect one module at a time to the supply. What happens?