We've been in this house for 8 yrs. This just started yesterday.We turn the shower on in the down stairs bath then we hear a banging sound in the wall and the shower turns off, we have to shut the shower off and then turn it back on again several times and it will correct its self, WHY and HOW can I fix this.

I don't have an answer for your question. But, I care that your question gets answered. By my posting a reply now, your question will get moved more towards the top of the list of questions needing answers. Hopefully, someone will come along soon with the expertise to answer your question.