Does it make the sound only when the 424 is engaged, or dis-engaged?
Also, check and make sure a small pebble or debris is not caught between your brake rotor and the plate behind it. I helped out a guy the other day in a Dodge 4x4 truck that was convinced his front differential was going out because of a loud, high-pitched sound being made any time the wheels/driveline was turning. I pulled off his wheel and found a tiny little pebble caught against his brake rotor. Problem solved. Surprising something so small could make so much noise!
Also, check and make sure a small pebble or debris is not caught between your brake rotor and the plate behind it. I helped out a guy the other day in a Dodge 4x4 truck that was convinced his front differential was going out because of a loud, high-pitched sound being made any time the wheels/driveline was turning. I pulled off his wheel and found a tiny little pebble caught against his brake rotor. Problem solved. Surprising something so small could make so much noise!