WHat you're describing is 'fret buzz'. Basically it means that the string is vibrating against a fret when it shouldn't be. What you can do is try playing different notes up the string and find where the string doesn't vibrate. That will be around the problem fret. One solution could be to get slightly thinner strings, or alternatively get the action of the string raised. I would suggest try the first route, as a new set of strings is relatively cheap. If the problem persists, take the bass into a guitar shop that does repairs and explain your problem. Also, it could be that you are playing the string a bit too hard. Also, are the strings new on? could be that they just need a bit of breaking in.