Chevrolet Repair: Front Differential of a 1998 Tahoe, axle bearings, high speeds

Question
My tahoe is making a noise that sounds like chirping.  I believe it is comming from the front differential.  I had it looked at and the tech thought it was comming from the housing.  The Axles move up and down, back and forth slightly not sure if this is a common thing?  Could that be the cause?  Someone has also suggested that it may be the bearings inside the housing but I am not positive there is bearings inside the housing.  If there is bearings in there can they be replaced or does the housing have to be replaced?  

Answer
Yes, there are inner and outer axle bearings.
Does the chirping happen all the time?
At low speeds or high speeds?
When applying the brakes, does the vehicle pull to one side or the other?
Does it quiet down when making a right or left turn?
There are a lot of things it could be, so, be patient with me as these questions I ask will help to pinpoint the problem.