I don't have a source for that, no - it's common sense. I imagine the reasons race cars are loud is simply that it's not worth the extra weight or complexity to

I don't have a source for that, no - it's common sense. I imagine the reasons race cars are loud is simply that it's not worth the extra weight or complexity to ensure the system doesn't waste so much energy as noise. The sci-fi angle I alluded to relied on hyper-science as the solution for ensuring that all energy within the system was used beneficially.