Nothing to do with understeer; the relative difference between the front and rear axle speeds, as determined by your relative tire pressures, takes the slack out of the center diff gear(forget which one) when you're decelerating. This is the likely cause, not the only one. Do a search and you'll get a better explanation
Understeer can be caused by a multitude of factors, one major one being our open front diff and 50/50 torque distribution between front and rear. I doubt your noise has anything to do with understeer.