Before I start, I want to thank all for your advice and help! Please bare with me, it's going to be a little long. Also I've no experience in plumbing at all.

House Age: 10
Water Hammer: No water hammer issue before the remodeling
Waster Pressure: between 70-75
PRV: No
Expansion Tank: No
Water Heater: A.O. Smith 50gl
Water arrestors: Two at the washing machine

It's all started few months back when we remodeled our bathrooms. We remodeled three bathrooms. Two at upstairs and one at downstairs. We remodeled one bathroom at a time. Here's the order: Upstairs hall way bathroom first, then downstairs bathroom, and finally the master bathroom.

The water hammer issue was discovered during downstairs bathroom remodeling. We noticed that the hot water came out really slow and weak (no pressure), it's barely enough to take a quick shower. The issue was resolved after the contractor fully opened up the cold water to the water heater.

After the remodeling done, we can hear the banging noise at every bathroom when you turn off either hot or cold tabs, showers, and toilets. The banging noises were located some where else, not directly next to the tabs, shower heads, and toilets. For tabs, if you close slowly then there's no noise. So I started searching and reading the forums in regards to water hammer issue. Here the things I have tried:

1. Bleed the air out of the system (tried many times but no success)
2. Replaced the Water Heater (No more water hammer from hot water tabs)

Here's my questions:

1. Should I install an expansion tank first and try to see if that will resolve the problem?
2. If step 1 didn't resolve the problem then should I install PRV and try to reduce the pressure to 60's range?
3. If above steps didn't work then should I install arrestors on all tabs and toilets?

I appointments setup already for getting the quote to install expansion tank and prv for the next couple of days.

Thanks.

They may have been as simple as a vertical section of pipe above the faucet take off from the line.

If you have single handle valves installing point of use water hammer arrestors, and a PRV for the whole house would be a good idea.

Higher than reacquired pressure can lead to increased flow speed making water hammer worse.

What's "ares tors"?

Also more updates:
1. There's no water hammer issue for the hall bathroom.
2. Still have water hammer issue on both hot and cold water for Master and downstairs bathrooms.
3. Had city inspector came out and did the pressure test, it's normal (70-75psi).

Is there any issues if I install the expansion tank without the PRV?

If I install the expansion tank only then what pressure should I set it to?

Most PRVs require an expansion tank also.

The PRV makes the system 'closed' and does not allow water to flow back into the system. Water expands enough when heated (even in a water heater) to require a way to release the pressure that would otherwise build up and can cause damage.

Just an expansion tank is not going to reduce you excess pressure, and may not have any effect on pipes hammering other than the one it is attached to.

Hammer arrestors are not very large and need to be near the valve that causes the hammer to be effective.
Sioux is a common brand.

As for installing a full size 3/4" hammer arrestor at WH location on cold side, can someone elaborate little more on why you need it since there's no hammer noise from or near the WH. No offense to anyone, I just want to have a better understanding on things because when comes to the actual installation, I have to have a plumber do that job and I don't want to shell out unnecessary money.

As for the original air chambers, I really don't know if we had any or not. I'll have to call up my general contrator to find it out.

But I do remember one thing when they changed the bathtub faucet, they had to remove/cut off some plastic part and replaced it with a copper thing to cure the water leak.

All advice is good, really broaden my knowledge on plumbing and I really appreciated!

The arrestors may work just fine near the valves that originate the water hammer.

They are designed to absorb the pressure wave created when the valve is closed quickly, instead of allowing to travel down the pipe and cause the water hammer.

They are normally installed near the valve for most effectiveness.

http://www.siouxchief.com/Resource_/ProductMedia/127/Tech Report - Expansion Tanks as Arresters.pdf

http://www.siouxchief.com/Supply/Arresters-And-Trap-Primers/Water-Hamm er-Arresters2/Hydra-Rester.JS766

There are many variables, proper pipe strapping and support is very important. Are the new shower valves anti-scald with integral pressure balancing spools, might one of the balancing spools be faulty? Is the system on a dual check backflow preventer? The code requires hammer arrestors on supply to quick closing solenoid valves such as dishwasher, clothes washing machine, refridgerator ice maker. These are 1/2" mini arrestors. A 3/4" arrestor is full system protection.