I know Car tech's listen to the engine, but I thought SP might have some interesting details to share? I like the idea of using our finely tuned hearing for something useful. You know in the real world, with real humanoids.
I've seen Das Boot, but I'm not sure car techs in 2011 America use the same tactics as German submarine techs in WWII?
You'd think it would be kinda cool to be rebuilding engines and stuff as a motor mechanic, but the good comes with the bad. If you happen to see someone driving along slowly rotating his head left and right, up and down and tilting side to side with an intense look of concentration - that guy is not crazy, he might be an auto technician acting like an owl trying to locate every single interior noise, rattle and squeek in a 3 dimensional plane. Quality control is a big issue to today's manufacturers. Also most mechanical failures will incur a mechanical sounding anomaly, stethoscopes (I just use a long screwdriver and stick the handle to my ear when I'm too lazy to fetch a stethoscope), microphones and headphones are used also when isolating noises that occur when driving.