Anybody who has undergone an MRI scan can tell you that other than the claustrophobia of being in an enclosed cylinder, the other bothersome part is the knocking sound that occurs. Here's a video (see below) that localizes where and why that knocking sound occurs. The bottom line is that the sound is due to a helium pump that disperses liquid helium in order to cool the wires that control the magnets down to -269.1 degrees Celsius. MRI machines work by generating a very large magnetic f…