08 6.4 motor "tapping" help

[smokeless_6.4]

ok, a friend of mine has a 08 6.4 he claims it has, bigger injectors, twin fuel pumps, and ported fuel rail. he is running the 315 sct tune. he recently had a new motor put in due to attempting to keep up with my spartan 6.4 he ran a low tune for about 3k miles then jumped it up to the 315. he said when he is at WOT at about 90mph he hears a tapping that sounds to be coming from the motor, as he described to me it sounds like a spark knock on a gas motor, anyone have any ideas on what this may be (is it running out of fuel or draining the pumps too fast) he said it does it also on lower tunes but nowhere near as much as on the 315 and he said it seems a little sluggish and slower off the line, and yes he is switching to Spartan thanks for any help