dont know about your year, but my mk1 suffered the same problem. i noticed it a week or so before it went in for its MOT, just a slight knocking or rattling. i mentioned this to the MOT station, which they said they'd keep an eye on. the car passed with no problems and everything was done up tight. then it started to get worse and at that point i jacked up the front and found there was a slight movement in the anti roll bar link, but i thought not enough to cause all that noise. however, i ordered replacements through ebay and whacked them on. HEY PRESTO, no noise. they seem to be a week link through the focuses. i was told you really need to change them as a pair, because the other one is not far behind and even though you say its the side you replaced, there could be a theory that the new one is being put under pressure from the old one. they are so cheap on ebay, that you might just as well change them as a pair. even dead easy to fit as well.