I listened to 'Cool, Cool' in its entirety. The hollow sound only occurs in the section following the exchange between Hancock and Dickinson. I'm sure it was intentional.
I had to do a lot of yard work last night, so I did not get to sample much of the Blu-ray. I mainly wanted to see how "Piddle Twiddle" came out, and was pleasantly surprised to see that all the footage matched so well; the sequence looked great.
Just skipping around, I thought "Cool, Cool...