2004 Chevy Tahoe Front Differential Bearing or CV Joint

I hear/feel a grinding on the front driver side. It is an all wheel drive tahoe with Stabilitrak. It does not make the grinding noise/feel when it is in neutral and coasting. It is not the brakes as it does not change when applying the brakes. One service center says it is probably the bearing on the input shaft of the front differential but they want to take apart the whole differential to see what other damage there might be. Can't they check the fluid for shavings without tearing apart the differential? Also wondering if maybe it wasn't the CV Joint and not the bearing on the differential as they said they have never seen thistype of bearing being worn out on a 2004 Tahoe. Any suggestions would be appreciated.