Spend some time with your bass to see how it reacts to how much force you use to strike your strings. I can get a rounded sound or the clacky sound out of the same string depending on how I pluck it. Clacky is wanted at times (depends on the song), I find to get that I use the tips of my fingers and pull towards the body of my bass. To get a rounded tone I pull my fingers into the palm of my hand, like when you make a fist. I played harp for a while, and found it's the same finger motion (not that you'll probably find a harp player around to demo for you!)
Might check your bass action, I keep mine a little higher so I don't clank accidentally. Have someone professiona/knowledgeable set up your bass

. Check your treble too, too high and it'll pick up the clank quicker. Which pickup up use (if you have more than one) also makes a difference.