I do tend to do knock checking for about 40-80 in 3rd then repeat in 4th then repeat in 5th.
But has done it as one power run 2, 3, 4, 5 so he is continuing with that for comparison reasons.
Next time I see him I will suggest he does some 3rd gear only then 4th gear only runs to see if the knock is still there.
I think due to his recent clutch change the gear shifts are quite violent, but his knock seem to appear at the end of run when the boost starts to drop off and the clutch should not have anything to do with that.

It is a bit odd but I am sure he will get to the bottom of it at some point.