A soft whirring sound is a motif that recurs throughout the last quarter or so of Infinite Jest. It makes its first and most dramatic appearance between pages 733 and 735 as the sound that an insane prospective Ennet House resident says can be used to distinguish between "real" and "metal" people. One reading of the motif would be that the whirring is the sound made by the kind of utilitarian pleasure-pain calculus that informs an addict's decision making. The idea is that when you're an addict, you're basically a machine (thus 'metal') in that your decisions are mechanical rather than subjective. When an addict makes decisions he isn't really choosing between options, but rather analyzing the options to determine which one is most likely to ensure his chemically induced pleasure. The "whine of Fackelmann's High Speed mentation" in the face of the Brown/Yale mixup on page 930 is a good example of addiction type thinking being audibly deterministic. Based on this analysis, the reason the Insane Ennet House prospy doesn't hear whirring when he listens to Marathe is that Marathe is a person capable of choosing unpleasure as well as pleasure (See his conversation with Kate Gompert on page 781), and thus isn't thinking in the robotic manner of an addict. The whirring made by the Infinite Jest the film's Ocular-wobble lens (939) can be interpreted as representing the infantile (in the freudian sense of the word) quality of the addiction-type decision making.