Check the plugs for salt and pepper, meaning black specs on the white part. If you can hear it its bad. Sounds like rice falling on tin foil or gravel hitting the underside of your vehicle. If you have loud exhaust then its harder to hear. You can also use a scanner to see if the computer see's it.
mild knock is a gurgling, sounds like it's running under water....
with what he said (salt and pepper) look for erosion of the electrodes for bad detonation (you should holy pistons by this point) and you may not just SEE the salt and pepper, so hit the plug with brake clean if it is really black to look for these signs. if you don't know what to look for, google.
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