Question

what were the reactions of the inmates to the sound heard in the hideout

Answer 1

If this is for Anne Frank: 
Whenever a voice came from the downstairs at inappropriate time i.e. when there was no one supposed to be in the building, all the residents of the annexe got scared as they thought that they either burglars or the police had entered the building and they xould get caught. So, they all were very frightened.