Hi, the knocking noise is caused by 3 things 1. Bent lifter rods 2. Rods needing a adjustment 3. Low on oil
The first thing you should do is check the oil and if oil is Okay then purchase the engine honey in a parts store and put it in the oil fill area which is suppose to quiet noisy lifter rods and if that doesn't clear it up then you will have to remove the valve cover to see which lifter is making the noise by starting the car and let it idle at normal speed and locate the lifter which is causing the knocking noise and if you don't hear it at idle speed then rev up the speed just a little until you hear it and once you locate it shut off engine and remove the lifter which is held down by 1 bolt and once you remove it very carefully remove the rod and run it across a flat surface to make sure it is not bent and if it is okay then clean it with a parts cleaner and make sure the hole in the rod is clear and replace it the put the lifter back on and torque the lifter the the required torque settings then put on a new valve cover gasket and check the oil again .
Note: Be very careful when ever you check the lifters with the valve cover gasket off because it can cause a fire if not done properly.
So good luck and hope you get it fixed
