Ripple voltage can be saw in oscilloscope. In audio circuit power supply, a audible(if frequency is audible 0 a 18KHz) ripple.
Most of times isn't main power supply but a ripple in circuit.
If capacitor is good, brown trace, without it, green.
If defective noise between green and brown, this audible riple (most of times 50Hz from main 240V AC power source) is amplified by audio circuit.