as Dan says, if its knocking replace the CV joint. The Boot replacement is easy i have just done one on mine yesterday for its MOT. here are a few photo of the replacement.
remove bottom ball joint, and caliper ( to save breaking the line ) make sure you remove the 30mm Hub nut before you jack the car up.
I used a stretchy boot, if you use one you always turn it inside out. plenty of lube on the cone. but not on the part your pulling
you will need, 18mm Socket and ratchet 30mm Hub Nut and a cone, WD40 and a new boot with grease oh and its messy!!!