Castle identifies the murder weapon as a 1959 Gibson Les Paul "flame-top" electric guitar. This model is one of the most highly prized and collectible guitars in the world.
Every time Castle "directs" the cameramen to do a hard fade to black and hums the sting, there is an actual hard fade to black.
When Castle tells the cameraman to "fade to black" and "add a hard sting" he hums a few notes. Those notes are the opening score shown with the Castle title card at the beginning of each episode.
Although Castle criticizes Zeke's self comparison to Pete Best, and suggests that Stu Sutcliffe would have been a better comparison, given that Pete was a drummer, not a bassist, Stu Sutcliffe actually left The Beatles on his own in order to pursue a career as a painter. Pete was let go and replaced with Ringo Starr, making Pete Best the better comparison.
When Castle says to the team that "pure speculation would be Swan purchasing thermonuclear technology to have a scientist make him an amplifier that went all the way to 12". It's a reference to the movie/mockumentary Spinal Tap, in which band guitarist Nigel Tufnel has a guitar amplifier that goes to 11 instead of the normal of 10. With the argument that they are "one louder".