humming noise and grinding

I know that a loose cv axle means that it needs to be replaced, but how loose is loose? Both CV axles on my 99 Chevy Malibu have a little bit of give. But the rubber covering at the joint is perfectly in tact and the give is only in one direction. My car is making a humming noise while I drive it, and makes a grinding sound while turning. My first guess was that it was the wheel bearing, but I want to make sure first that it's not the CV axle.