Most valvetrain noise can be considered more of a clatter than a knock. One thing that may help is to keep in mind that a knock will occur at the same number of revolutions as the crank while valve noise occurs at a much higher frequency. Listen to the noise carefully at low idle and see if it sounds like it is knocking at the RPMS or much more often.

There are so many things this could be, and without hearing the knock it is hard to diagnose, especially with no poor running conditions. Keep digging, you will find it