Variable Audible noise in flyback TNY278
i have designed a flyback converter using TNY278 controller. input voltage 230v and output spec is 12v / 1A. in no load condition there is a little audible noise that can be neglected but when the load is added to the output the frequency and volume of the noise changes. in different load conditions i hear different frequencies. i suspected that there is something wrong with my feedback loop. would you please help me
i have attached the schematics of my converter.