Buck converter, squeaking/whining inductor

The solution to solving this problem is adding a negative feedback, as explained in this video https://youtu.be/wNnOfF1NkxI?t=1584. Firstly I added a capacitor between the output and feedback pin of the TL494, it seems to have solved the issue, but it doesn't work as good as adding a proper negative feedback. I have done some tests, that prove this: At first, I increase the current from 0A to 3A and then I change the oscillator frequency from ~170 kHz to ~20 kHz and then go up to the "crash" (I suppose) of TL494 ⇒ beyond 300 kHz and then return to ~170 kHz. Yellow trace - voltage at oscillator capacitor, Blue trace - current flowing through inductor. The inductor now is not whining but hissing, it depends on the core used, because when I tried with EI, it was less noticeable (during the night the tape has loosened and the inductor started squeaking, now I am experimenting with nail polish as a way to glue the core and still be able to take it apart), This test was done with a factory glued EE core. The screenshot of a "spectroid" app is done when the output current is at 3A and at the bottom You can see the 20 kHz moment and at the top 300 kHz.

Negative feedback + capacitor https://youtu.be/S9KfA9NNXkE

Negative feedback https://youtu.be/h1AN7rQTDa4

Capacitor https://youtu.be/7h7OzDj9q8Y

Nothing (initial problem) https://youtu.be/nVOfPynJRGE

By negative feedback and capacitor, I mean:

Later I will check if my push-pull MOSFET driver works fine now. If there is a need, I can do a more advanced recording and show the frequency generated by the inductor corresponding to the oscillator frequency.