Welcome, I am Chris (aka-Moose)
Noises are tough for use to diagnose not being there to hear it. If you could make a you tube video that would help. Normally a knock if its for sure coming from the engine, is not good. A knock comes from deep in the engine from a piston wrist pin, rod bearing, or main bearing that has failed. Things outside the engine that can make a knock are the torque converter and exhaust baffles. An internal engine failure like this normally is from poor oil maintenance but can also be caused by age, mileage, high load or rpm, or just a failure with no reason. An internal engine knock 9 out of 10 times means a replacement engine is required.
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