Why should they support the audit? What are you going to do for them? Or, put another way, why are you doing the audit, because some schedule and procedure says you have to?
I'm still amazed, after over 15 years of training internal auditors, that some non-quality folks are expected to 'get it', about audits! Why should they? Did you do anything to sit down and plan and prepare your audit to be of value (and I don't mean heading off a non-conformity from a CB auditor) to the Manufacturing management?
If any of the answers to the above questions is anything like 'no', don't know', 'why?' or 'ISO says so', then you need to do something to answer the questions in a proactive, positive, action oriented manner, to gain their trust and support for the audit program.
And then you need to deliver an audit result they can clearly articulate as having been of value to them - not what you think is beneficial, what they say it is!
Oh, this is not personal, just my observations of why internal audit systems fail (and let's face it, this is a failure) based on over 15 years of hearing and seeing the same things!