I don't know the amp but I do know the symptoms, on rare occaisions it can be caused by a dirty volume pot, but due to the nature of it only occuring in class A, I would suspect due to the high bias current/voltage, MOS/Tran that the coupling caps if they are there are going, or the main power supply caps could sag and cause the same problem.
I can't speak to the amp and tell you to repair it or dump it.
loon
I can't speak to the amp and tell you to repair it or dump it.
loon