What is this noise coming from my wall ?

There is a strange noise coming from my wall. 

This happens every day and generally starts after about 14.00.  This happened last year also but stopped in the winter and started again a few months ago.  There is no sign of any animals or anything else gaining access through the outside wall.  If I bang the wall the noise doesn't stop or startle whatever is there so it is hard to tell what it is.  I have tried to capture this in the attached files.  

Does anyone know what is making this noise ?

I want to make sure there isn't a protected species in there before proceeding with any further investigation

Noise from wall 1.m4aNoise from wall 2.m4a