First of all, shut down the amplifier, wait until it dies down really off, and then disconnect the RCA input cables at the back of the amplifier, so the amplifier is only connected to the speakers.
Turn the amp on again. Does the hum go away? If so the problem is not the amplifier, but the connections/cables ahead of the amplifier.
Is the hum coming from the chassis of the amplifier or from the speakers? If it is from the chassis, a HumDinger may help. It will not help if the hum is from the speakers only.
We have seen hum caused by use of exotic interconnect cables, such as those claiming to be unshielded or "one way" designs. These often pick up excess hum or cause ground loop hum. Try the amp with plain old cheap simple coax RCA cables.
If you still can't find the cause, please call me for help. 651-330-9871.
The problem most likely is not a failed capacitor. We have yet to have that happen on this series of amplifiers.
Frank Van Alstine