I really need some help diagnosing this problem. What started as a "playing card in bicycle spokes" type of sound coming from the top part of the engine, has now evolved into a "chopper" motorcycle sound immediately after I fire the car up. The idle is bad, feels like its gonna die, and the noise is incredibly loud, and sounds like a motorcycle at both idle and wot.
Could this be a cracked exhaust manifold?? What else??