If I wanted to listen to a newer diesel loud and clear, I'd be breaking the law and EPA guidelines. All three pickup brands making one tons have decently quiet diesels, and Sprinters are no louder than a gasser. To boot, here in Texas, the DPS (similar organization to California's CHP) actively will pull, smog test on the spot, and scrape off inspection stickers of any modified, smoking diesels. (One can thank the coal rollers for that.)
Older diesels could be idled indefinitely, but a newer one will end up having the DPF plug up unless a high idle circuit is put in, and those particulate filters can get pricy. Plus, new diesels, when they break or wear out, it costs a lot of cash. The high pressure fuel rails give excellent MPG... but it takes a lot of engineering to do those right, and injectors are not cheap.
