Hi.
The buzzing sound alone may have been caused by a bad grounding, or a contact, but the clicking noise makes me think that there may be a faulty component, and that the click is coming from the protection circuit inside the receiver.
Test the unit on a different socket, unplugging any other connection.
Double check speakers and all connector. Even a short caused by a copper fibre on any of the connector will cause same problem.
If there is nothing evident in connections, and if connecting to a different socket does not help, then there is an internal fault.
In that case the unit must be tested thouroughly by a technician.
Since the repair won't be less than $80 ( could be more if troubleshooting takes time), you may decide to replace the unit, rather than repairing.
Here a broken unit for spares:
SA-AX720 stereo Receiver tuner, amplifier -100 watt.
If you want a second hand Technics to fill the gap in a technics rack, check the links below.
Technics Sa-4046 Technics Sa-gx100Receiver Sa-ex110Technics Sa-500Call Technics and ask a quote on repair, sometimes the manufacturer can also offer a deal, exchanging older unit for a discount on new one, even out of warrany. Asking does not cost anything.
Do not forget to leave feedback.
Thanks.