uc3842 transformer noise
If you can hear the noise, I suspect the power supply loop is oscillating at some audio frequency.
To check that, connect a scope to the output and see if there is some ripple at low frequency; almost sinusoidal, at perhaps a few kHz.
You can connect the scope to the output of the error amplifier to see this signal; normally the output of the error amplifier should be just DC, but if the loop is oscillating you will see the signal described above.
Or, connect the scope to the switching element and check if you see a large jitter on the leading or falling edge. Some is normal, due to the 50 or 60Hz input ripple, but if it's excessive, that is an indication the loop is oscillating.
If you do not have a scope, try slowing down the loop, by connecting a fairly large cap across the feeback network. If the noise goes away (or at least changes its pitch dramatically), you know the loop was oscillating. You can then redo the loop compensation. You can post the schematic and I can suggest the changes.
Normally, when you design a power supply, you should measure the gain-phase characteristic, but that requires a gain-phase analyzer, an expensive piece of equipment. If you do not have it, you need to calculate the loop and check the transient response to see if you get oscillatory response. That would mean the loop is close to being unstable.