if your getting the noise when you go over a bump then you can be sure it's the ball joint and i'd advise getting it changed asap, piece of urine to change takes about 5 mins and its only four bolts and the ball joint is cheap too, about a tenner. to check to see if it is your ball joint just turn your steering wheel until your wheels are facing out and look at the bottom of your suspension strut, if it looks rusty and dry then its a definate but to be extra sure jack up the side of your car up so your front wheel is in the air and try to move your front wheel in and out.
take heed tothis warning ifyou don'tcheck it soon and fix if needed then the next time you go over a pot hole or tossy speed bump, your front wheel could end up down the side of your car and you in a bush or worse in hospital and your car down the scrap yard
