Back in the Keswick tunnel

 We were back in the tunnel on the Keswick to Threlkeld track. I was able to notice that there are echoes this close to the end. I wondered whether it was the cladding but it did seem to be the same even into the brick section.

However, as reported previously, the mid-section was acoustically dead. So is it an end effect? Is it an echo more from the change in acoustic impedance rather than from the walls?