Required or not, I don't see why you wouldn't WANT to audit the internal audit process. It's an important function of a business (if it's done right). Don't you want to make sure it's being done as stated and that there aren't any glaring holes in the process and maybe even see if there are any improvements that could be made? We just did an internal audit on our internal auditing process and we did it just the same way we do all our other internal audits.