If there are now 2618 pistons in the motor you will need to turn up the knock noise thresholds per cylinder. >> EDIT - Just saw you turned up the noise floor already. You could keep turning it up until you hear real knock (like Joe mentions) to establish whether you have real knock or not - the 2618's will handle it ok.
It depends whether they have offset pins as to how noisy they really are. "Dont you just love the sound of piston slap in the morning"