Did the piece of carbon come through the spark plug hole or was it sitting under the shroud, (valve) cover?
Are you sure it was carbon?
I ask because carbon is soft in most situation unless it is built up on top of a piston.
It would be un-likely for it to make a rattling, "metallic" type sound.
If it did come from under the valve cover, it is dis-concerning that that much sludge or a piece of carbon ended up their.
If the carbon came from a spark plug hole, that is build up on top of the RPMs or not using a good fuel system cleaner.
If it came from under the valve cover, it is either a piece of metal or sludge from not changing oil and not running fuel system cleaner.
Or if you have not kept your ant-freeze serviced, you could have a blown head gasket causing damage.
Generally it sounds like motor damage, lack of maintenance or something there-in.
Does the vehicle have any performance problems?
How long did it rattle before you had it looked at?
If you ca get another piece of it, I would look at it under a good light and magnifying glass and maybe even try to clean it off to see if it is not carbon covered metal.
Let me know how it goes and I will watch for your reply.
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Wednesday, August 24th, 2011 AT 11:22 PM