Service Speaker Porblem with i9082 (How to get back stock ROM) For Samsung Service

I;m currently using CM'11 ROM and recently have been facing some problem with the Speaker.

Please tell me steps on how to go and get back to Stock so that I can give it to the Samsung for Service since it comes under Warranty.

I don't think they wouldn't service if it has been Rooted so need to unRoot and Stock ROM or anything else I need to do?
Samsung Galaxy N2 / N3