well the tear in the rubber boot isnt going to make it knock but if there is excess play in the joint its self because it got dry and worn then it could cause a knocking noise , if its worn id replace that first as its going to need doing come mot time anyway , if the knocks gone it was that, if not check antiroll bar bushes / wishbone bushes and shock / top mount etc.... also worth checking trackrod end and tie rod from steering rack for play as these could also give a 'knock' effect when going over bumps etc
