I have a 2009 Vibe, 2.4L AWD, automatic transmission.
It's has started making a distinctive buzzing noise when I accelerate. It's almost like a really fast spinning propeller like noise. Seems to be coming from the engine compartment. I only hear it when the engine is wound up to accelerate, such as on a freeway on ramp to get up to speed. Otherwise there is no audible noise outside of normal engine noise.
Ideas? It almost sounds like an exhaust leak, but I'm just guessing.