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Wanted to add in these cases until the source of the noise is known and what it means has been determined the less the engine is run the better. No noisy engine ever got better with more run time.

My usual advice is the engine should be run only under the direct supervision of a qualified tech as he seeks to diagnose the noise source.

Hi. The noise has the aspects of an exhaust leak. But I'm not qualified to make that call. You need to get the car to a professional mechanic one who knows these cars very well. He will get the car on a lift and from under the car locate the source of the noise. Exhaust, possibly water pump, or from some other source.

No brass in the car. Bearing shells have a copper layer. But not likely the engine is eating its bearing shells. More likely what you saw was not brass but hard composite plastic from one or more rails that cover the several chain guides. A bit of plastic from these is normal.