a new noise after installing an expansion tank

[jlp]

I had a hot water tank blow it seam somewhere it was leaking or should I say poring water out of the outer jacket. It was covered under warranty. but i chose to install an expansion tank on the cold water inlet of said water heater, now I have a rumbling noise when I run water and the pressure fluctuates. How can I stop the madness?

[valveman]

Let some air out of the expansion tank.

[jlp]

Let some air out of the expansion tank.

that did not help

[valveman]

OK, then you need to check the air pressure in the tank. Turn the water off to the house and open a faucet to drian house. Then check tank air pressure with a car tire gauge. You need about 30% less air pressure than the lowest water pressure you see in the house.