How do I know if my front wheel bearings are worn out?

 

If it has play or humming sound. Humming could also come from tires too.

 

Extremel rare for both to go simultaneously.
You'll hear, and feel, a low rumble when going around a curve. As the car turns the majority of the turning load is transferred to one one of the front wheels. If you hear it when turning left the pass side bearing is going bad and vice versa...

 

They get worse fairly quickly. I bought my LS with a sketchy left front bearing and within 6000 miles it was completely shot to hell. They're super easy to change though. Caliper off, rotor off, 4 17mm bolts in the back of the knuckle and it'll pretty much fall out. The rears are a pain in the *** though