TPS64203: switching freq of the TPS at almost no load for both boards

Hi Support,

Some questions regarding the switching freq of the TPS at almost no load for both boards. Can you adv the reason?

I attach the waveforms for Board 5 and Board 7 for the VDD3.3.V.

For Board 5, the sawtooth frequency of VDD3.3V is 92.59Hz. 

For Board 7, the sawtooth frequency of VDD3.3.V is 416.6Hz.

Thanks.