Short answer: Not necessarily (spelling?)
Long answer : One might be more worn than the other side. But they're both (presumably) about the same age, so will have similar levels of wear and tear. So on that logic, the "good" one may fail sonneish. I personally wouldn;t rush to replace the "good" one if it wasn't damaged. I'd wait. Spead the expense apart from anything.....
If the noise isn't too loud, it may also just be the seal, not the whole thing that needs replacing (had a Ford Laser (=US escort) and the boot went on one side, but the whole CV was gone on the other. Only seal needed replacing on one side, whole thing on the other)
