The CA201 uses a big toroid for it's power tranny, - it shouldnt' buzz at all. I have a CA200 which is basically the same amp - no buzzing, humming. The tranny is encased in a machined aluminum cylinder so even less reason it should be making noise. Something is definitely up. Caps should need checking too, could be one is bad. This amp should be dead silent when nothing is playing through it.
-Ed
-Ed