Daleford

Can't find this noise on our 05 GT. Only hear it under load as you turn to the right. It is a growl that travels through the rear chassis. Had a Ford mechanic look it over and he thinks it is a left rear noise for sure. For example, something like the axle moving just enough to send the rotor into the ABS sensor or the tone ring rubbing on the end of the axle housing. [it is neither of those]
Someone has suggested differential clutch pack causing this.
Any thoughts?