A No-Rough-Stuff Type Deal - S1-E7
Trivia: Bryan Cranston, Aaron Paul, and Raymond Cruz reprised their respective roles of Walter White, Jesse Pinkman, and Tuco Salamanca for a Super Bowl commercial for Popcorners, which was reminiscent of the scene where Tuco tried the blue meth for the first time.
Answer: For one thing the engine running the pump isn't that loud. The characters have conversations at a normal volume without having to scream at each other. Even if the conductors could hear it, there is no reason they should care or be suspicious. It just sounds like an engine running in the distance and they don't care enough to look for what is making the noise. At that very moment there is also a kid riding a dirt bike in the area. Engine noises are a very common thing.
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