creaking Feeling/almost small vibration feeling when my snake moves

Hi.

I have a corn snake that is around 5 month old.
He eat one 3g pinkey every 5 days, and he Just finish shedding. This time it took 2 month for him to shed.

Back to the question.
When i hold him and he moves around my fingers i can feel the snake body have a creaking Feeling, almost like a very small vibration feeling from him everytime he moves.

What could that be?

Thanks for answers.