Engine tapping noise 95 Mustang

95 Mustang 3.8 V6. New purchase. I recently noticed an engine tapping noise but only under certain circumstances. No noise when engine is in idle or general driving conditions. But I hear the metal tapping noise when in park and rev up the engine or if I accelerate fast after a stop sign and get the engine up to 2500 to 3000 rpm before it shifts. No noise below 2500 rpm. I decided to flush the engine and change the oil. When I turned the car on after this, the engine made that tapping noise but only for two seconds until the new oil had a chance to recirculate. What's the problem, bearing? rods? rockers? valves? I don't think its injectors or converter noise. Is it worth getting a professional flush of the engine to clean out any old oil sludge? Any additives to try? Synthetic oil?

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