TPS54231: There is a shock wave on the TPS54231 output 5V, and the audio frequency is on the audio, so the sound can be heard from the speaker

Hi ：

      I use TPS54231 in my product,the chip input voltage between 20V to 26V, the output voltage 5V for  a digital amplifier power supply(the digital amplifier PN is  VA2101) .The horn connected to the amplifier is 25. 

Problem: there is a shock wave on the TPS54231 output 5V, and the audio frequency is on the audio, so the sound can be heard from the speaker.

1,、Adjust the  C27,C28 ,R36 value,  have no effect;

2、If I add a 510 Ω  pseudo load on the 5V, the fault disappears.

3、If adjust the input voltage for TPS54231 lower than 24V, the noise will disappear, as long as the input voltage is higher than 24V, 5V shock wave back again.

In the product, I can not add a  pseudo load. Do you have a good solution to this problem?Thanks a lot！