I think you are missing one point though. If people decide to consume more or less at some point, it will change the money they can save and therefore the money there will be availabel for investment. In an extreme case if people got fed up of saving and increased consumption a lot, therefore not being able to save interest rates could raise even when growth was happening. Obviously, since people is consuming like crazy and not investing for the future, future growth would suffer, but theoretically you could have interest rates raising infront of strong growth. But such a change in behaviour from everybody at the same time is not probable at all (in a free market).