As people who know a fair amount about me are aware, I trained dogs professionally for a short while. During this time I became very familiar with the principles of operant conditioning. For those less familiar, these are the principles seen in Pavlov's famous findings where dogs would salivate upon hearing a bell which was rung before feeding, even when no food was present.
When I lived in Chicago, I spent a full year living in a studio off of the red line - when I say "off of," I mean my window was less than 50 feet from the track. Because the building was nothing but studios and the walls were terribly thin, noise during play was always a fairly large concern. I had a friend who was into some rather brutal CBT and could not only easily push me to my "reasonable" limit and beyond, but still want more even with me there. I was hoping to try and experience as close to legitimate panic as possible while inescapably bound, but I'd get too noisy during this level of abuse.
Eventually, in order to mitigate possibly having my neighbors complain, I told him that any time the train passed by he could wail on me as harshly as he wanted since the rumble would mask my howls. "Could" quickly turned to "would," and it was set up so EVERY time the train passed he'd wail on my balls until I was screaming.
Now, back to Pavlov's dogs. Much as the anticipation of food made the dogs salivate, sure enough the far-off rumble of the train became somewhat of a trigger. Once he got me to the point where I'd panic, after a few repetitions all it took was hearing the train in the distance to make me break into a cold sweat and instinctively try to protect my balls.
Ever since moving out of the studio it always saddened me that I can't duplicate the scene again - somehow using some form of a random noise generator just doesn't seem as thrilling. The conditioned response ought to be identical, so anyone looking to duplicate it may have luck with a fade-in track of some sort on random in iTunes or similar.