Answer:
No. You are obliged to notify the consumer customer of the results of your investigation within 3 business days after completing the investigation. If you determine that no error occurred or an error occurred other than the one the customer claimed, you have to provide a written explanation of your findings and inform the consumer of the right to request the documents you relied on.
Although that's the only instance in which the notice must include written information, providing and retaining a copy of a written notice can be an effective way to document that a require notice was given.