Ummmm what is missing here is that you only get "knock" (dangerous pre ignition, uncontrolled explosions, too lean, too advanced ignition for the load and conditions) under higher loads.
You are not going to near engine knock driving around normal with the stereo on. If you heard actual knock even with the stereo off under a WOT pull, things are pretty much done. On a Dynapack dyno with no tire noise it takes at least a 6 -9 count of knock to actually hear it _if_ you are listening to it. This noise is just a little single "tink" or series of "tinktinktink".
Now if we are talking about a motor with a knocking noise that is different. If a water pump pulley is loose and rattling, if there is a piece of a spark plug stuck in the top of the piston and hitting the cylinder head, if you have a bad rod bearing that is flopping around on the crankshaft.. that is a knocking noise that you would hear just listening free revving the motor or driving in a parking lot.
If I read correctly this is a recently purchased used car? What is the history on it? Any warranty?
If the car was here at the shop making rattling knocking noises on a free rev we would:
Listen with a stethoscope (or a long screwdriver, touch the srewdriver tip to the motor, listen to the handle) to try to generally locate the noise. Top up in the cylinder head, bottom end, timing chain side.
If abnormal noise up in the head take off the valve cover and have a look.
If in the timing chain area have a look at the visual stretch indicator.
If bottom end, cut open the oil filter and look for bearing debris. If gold flakes that is bearings. If aluminum paste looking then that is the oil pump dying.
If you suspect it is an accessory (water pump, alternator, power steering pump, A/C compressor) making the noise, you can take off the serpentine belt and run the motor briefly. If the noise goes away then it was something that the serpentine belt was turning.
There is a possibility that something in the transmission is making the noise also. You or someone that knows cars needs to get to the bottom of this as soon as possible. There is only so much the internet can help you here.
Mike W
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