Buzzing gets louder with the volume control - noise is picked up in the front end, radio or inputs.
Are you using the radio tuner or plugging in an external sound source, phono or tape?
If radio, unplug all wall warts, phone chargers, printers, laptops, etc. Also turn off LED lights in the room. If that does not affect the buzz, try the stereo in a different room, different outlets. You are checking to see if the noise is external, easy fix in most cases.
See if the noise changes with different sound sources. That might indicate an internal fault, maybe why it was for sale.
