If your neighbor calls the cops because of suspicious activity, they have an obligation to investigate. Its the job that the citizens pay them to do. If you are doing something illegal, don't answer the door. They would probably rather you didn't answer the door as that means more work for them. If you are just home brewing, I'm sure most cops know that it's legal and many cops probably home brew themselves. If they aren't sure about the legality of home brewing, or don't know the difference between home brewing and distilling, I say take the time to show them around and educate them. They would probably appreciate it and find it interesting and would probably help out the next home brewer that has the cops called on them.