Audio Noise from TOP243Y SMPS

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I am designing an SMPS with TOP243Y for 4.2V, 2A. Without load, the output gives 4.2V. But when load is connected and drawing 0.6A of current, audio noise is coming out from the circuit. Output voltage is still 4.2V. Please let me know the solution.
Hello, what sound is coming and from which part of circuit? is it transformer,i suppose to be. Check the transformer design again for inductance, leakage inductance. Also, if u have High voltage probe & current probe for CRO, please ensure that u r operating it in safe limits.i.e. Drain to source voltage less than 700VDC & drain current to 1.43A. for more details, pls mail me at along with your schematic.

Hello gurung_vishwas1

Please post some scope waveforms of the drain voltage waveform and output voltage. That will help narrow down what's going on.