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.

Do you live in city or country? If on well water then could have air in line. However the knocking you hear is the pipes on the studs they are supposed to be anchored to they have probably come loose and are moving in the walls.

I too, am interested in finding out if this is on a well or city water. If on city water is there a PRV, ( Pressure regulating valve) involved. If on a pump system is there air in the lines to the point of the faucets "spitting" at you?
Do you get a "bang" when you close a faucet? Let us know, regards, Tom