Depends on what car you're talking about. Front wheel drives are harder to detect than rear wheel drives on the front wheel, and the opposite on rear wheels. I've had several on the front end that didn't make any noise but pulled the scar in that direction, and felt loose in steering. I've had a couple of rear bearings on RWD cars that didn't make noise, and were only found when I was servicing the brakes. If you have any doubt, especially on the front wheels, change them, failure at highway speeds could be deadly. If you are able to do the work yourself the bearing shouldn't be too expensive. But in the end, what is your life worth?