Plumbing and Piping - Water pressure problem

Replaced the basement laundry tub, along with new wired flex tube, and shut off valves. Every since the hot water pressure in the house varies. One thing I noticed when replacing the laundry tub valves was that one of the copper pipes seemed loose. The elbow could be turned easily. I had to re-solder a new piece of pipe to install the valve. I didn't use too much solder and joint has a nice even bead of solder. That solder wouldn't affect water pressure.

Water is by city line. Main stops valves have been replaced before and after water meter. Water meter is old and is due to be replaced. Stop vales are ball cocks and are wide open.

When taking a shower the water pressure drops off if the washing machine or dishwasher is running. All taps in the house have pressure drops. Not just the shower. When taking a shower the anti scald valve works. The temperature of the water does not change, just the pressure.

Pipes are noiser than usual. Not a banging sound. Just a louder sound of water running through the pipes.

I tried bypassing the water softner and there is still a problem with the water pressure.

The valve to the water heater is seized. Water heater is approximately 6 years old. It is a rental.

Should I have the water meter replaced? Could it be the water heater? Where is the pressure reduction valve from city pressure to house pressure?

Thank you for your assistance

What is new wired flex tube and how much of it, size, and how come?

You really believe that the pressure has now varied because of this work? And actually, technically, your pressure may be the same, but restriction is causing a volume issue.

Regarding the sound inthe pipes: Sounds like a restriction causing increased velocity of water in the pipe or fitting(s)

Pressure reducer? Maybe you don't even have one? Do you know if anybody around you has one?