My factory built car had a noisy diff.when it went back for its 500 mile service I complained about it [i think it totally spoils a great car] I was given the Tadts treatment.
For the next service I took it to Clive Kenrick, He agreed with me,phoned Caterham and they consented to a new diff. being fitted under warranty.What a result ! actually the new one wasn't much better than the old one, but I don't mind so much ,pleased that Caterham at least made the effort.