I have a Seduction with C4S upgrade. There is a rushing sound with a periodic thumping in one channel. It still passes audio. Switching tubes has no effect. I have reheated all the joints on the C4S board, the socket of the offending channel, and the other end of the components connected to that socket. A1 measures 94.7V and A6 measures 83.3V. Any ideas?
Thanks