It's usually the potentiometer needs cleaning (spray-can electronic contact claner). (The volume control)
The fact that you get this noise when you adjust the tuner dial tends to tell me you may have another problem, as potentiometers are not used for tuning.
I'd use compressed air to blow-out the dust from the chassis, check your cables to the speakers (make sure they're fully making contact, and move them around a little to make sure one of them isn't causing the issue).
I'd clean that volume control potentiometer, and all of the other push-button switches accessed on the front panel.
Most of the time, that would solve a problem like this.
Make sure the unit is unplugged while doing this, and yes, you'll have to take the top cover off the chassis to access the switches and pots inside.
If this is beyond your scope of new experience activities, a repair shop will be happy to take your money to do the same thing.
