PJ's got a good point too. Given that providing examiners with a list of appropriate contact personnel is both helpful and prudent, you simply cannot control who examiners talk to.
All employees should understand what the purpose of the examination is; that the people involved are examiners, not auditors; and that involving their supervisor in conversations with examiners is expected. Employees should emphatically be told that "I don't know" is an acceptable answer and far preferable to a guess. Auditors who rely heavily on interviews contribute to helping employees develop the necessary skill set.
We had an employee, fairly described as a PITA, who gave an answer about our processes that was blatantly wrong. We spent the rest of the exam trying to kill the issue and had to repeatedly emphasize that she was not on the list of knowledgeable employees we had given them, the answer was simply incorrect, and her answer reflected nothing more than her unending need for attention. In the CYA move of all time, the examiner raised the issue in the exit conference and then noted that there was no evidence that the statement was correct and the bank had denied it.
It turned out okay, but it was a huge waste of both the bank's and the examiners' time.