In addition to the above we have spoken to Gigabyte for clarification of there process and they confirm:
I am informed though that the item was cleaned before inspection and tested twice, where it is left on test and fault diagnosis is run. If it passes the engineers set out testing procedure, it is then handed to our tester who carries out the same sort of procedure.
It could have been this cleaning process which resolved the problem, IE the fan could have been affected by dust reducing the reliability and thus cleaning it resolved the issue.
I can only speculate but obviously something has resolved the problem that was there initially.