DM, the thread you posted on is more than two years old. Many people are not a fan of galvanized due to rusting/iron deposits.

Could it be water hammer, when the pump cuts off.

Fish, this post is three years old. It's dead. However, keep posting. Involvement is a good thing.

jlisenbe, sounds like thread age is important to you and you don't want people to post on old threads? Why is that? While the original poster may not be participating any more, it seems to me that more people with the same or a similar problem will be along.

It's OK with me. People just need to realize that it is unlikely in the extreme that the original poster will reply or even read their post. If you read this site a few days, you will find that 99% of the posts are for current threads. But again, people are free to post if they want to, and they certainly don't have to worry about my opinion on the subject.