Toyota Repair: noise at highway speed, front wheel bearing, bad wheel bearing

Question
Hello,
I have a '94 corolla with 61K miles that I just bought.  It makes a faint noise and vibration at 65 MPH plus.  A receipt in the glove compartment indicates that the left front wheel bearing and inner/outer seals were replaced three months ago.  I raised the vehicle and could not feel any play in the wheels.  I also switched tires with another car and the noise is the same.  As I switched the tires, I noticed a singe ball bearing on the floor beneath the left front wheel area.  Is this from the wheel bearing?  Could a faulty wheel bearing be causing my problems?
Thank you in advance for your help.

Answer
The wheel bearings are sealed and I don't know how a single ball bearing could have fallen out, not sure what is going on here, the noise and vibration could indeed be caused by a bad wheel bearing but the problem is more likely to be caused by a faulty differential bearing in which case the transmission assembly has to be replaced, have a toyota dealer check it for the noise.