yea the sound was in tune with the engine, and it was after a period of pretty much hard acceleration. The sound was loud and went away after reving the engine a few times, but then returned and went away. Someone said a screw might have got sucked into the combustion chamber...that kinda sounds like what happened and my cel is on and blinks when i drive the car (which i am not currently doing much of). And when i do drive it it definetly feels like there is only 3 cylinders working because the car shakes moderatly when i give it gas, its almost like a sputtering. If thats the case then the 2.0l engine that mazda uses is garbage because nothing like that should happen on a 4cyl car with only 50k on the odometer. Even if i was driving it hard it wasnt at redline and it never had a problem taking it before.