How to fix reverse water hammer?

There is a single loud bang when the cold water is turned on in the bathrooms or kitchen. I believe this is reverse water hammer.

Any way to fix it? I haven't found much on the topic from Googling.

Have you lived in the house for a while and this is a new sound? Has there been any plumbing work done recently? I've never heard of "reverse water hammer" so maybe you just mean water hammer. If it's happening when any cold water is turned on in the house the sound could be from a number of things. It could also be a damaged gate valve somewhere on the piping or a failing ballcock on a toilet.
This sound only happens when cold water is used or is hot water also hammering? Is it happening when the water is turned on or off or both?
Have you checked your water pressure? Do you have a regulator on the water service?

We've lived there for a year, we had major renovations including having most of the house re-plumbed since it was built in the 70s and had a lot of old under slab plumbing. It only happens when the cold water is used, never hot. The sound only happens when the cold water is turned on, a single loud bang/thump sound.
We have a pressure regulator and PSI to the house is around 60.

How would I know if it's a toilet ballcock causing it? The upstairs guest bathroom toilet sometimes gets stuck in the open position, so if any toilet is failing it would be that one.

sounds like a loose pipe slapping against a stud when the water turns on

Me and the plumber narrowed it down to the sound coming from the pipes in the garage, he opened up the walls and made sure everything was tightened down and found a loop of sorts/extra piping where it wasn't needed in the cold line, so he cut out the loop and made the lines as straight as possible. The sound is now not as loud but still happening and now it's random instead of everytime.

So I'm kind of out of ideas and so is he.

their is another place...you said you had 60psi
turn it down, see if it helps. most houses are 45-50 psi

We tried that as well, lowered it to 45 and 50, it went away for about 30 minutes and then came back. It has him scratching his head he's never seen something like this.

their is another pipe slapping around..going to be a pita to find

Do you have a check valve on the water heater? Try turning off the cold supply valve to the water heater. Your man cold water shut off a ball valve or a gate valve? Make sure all your angle stop valves to your fixtures are open all the way. Do you have any automatic sprinkler systems tied to your service before it comes into the house? It bangs when you open the faucet so I'm thinking maybe a check valve slapping shut when
the water flows

There is an automatic sprinkler system tied in before the house. How would I check to see if I have a check valve on the water heater?

Mr_David said:

Do you have a check valve on the water heater? Try turning off the cold supply valve to the water heater. Your man cold water shut off a ball valve or a gate valve? Make sure all your angle stop valves to your fixtures are open all the way. Do you have any automatic sprinkler systems tied to your service before it comes into the house? It bangs when you open the faucet so I'm thinking maybe a check valve slapping shut when
the water flows

Click to expand...

I just talked to the plumber and he says there is a check valve on the water heater because we have a recirc pump/recirc line.

Could it be the check valve causing it?