When we turn on a shower, or flush a toilet, or turn on washer (Not necessarily all at once), we get this loud banging sound in our walls throughout or home. It doesn't matter if it's the cold or hot water. We live in California, moderate weather, two story home. This has never happened in the past, just started about 1 month ago. It happens periodically, not always. When it happens our water pressure gets very low. Please give me any advise. Thank you.