Water Heaters - Water heater noisy

I have 40 gallon gas water heater in basement of brick ranch.
When my wife runs the clothes washer, the water heater makes a terrible noise.
It first is loud noise like a water hammer, then continues getting less. I sounds like bubbles rising in the water heater.
It sits about twelve feet from washer, which is also in basement.
There does not seem to be any air in system when you open any faucets.
I've even plugged pressure relief temporarily to see if it stopped, but it did not.

When is the last time you drained and flushed the water heater? Your sound description is not familiar. I am guessing that since it is heard when using the washer, someone is in the same room with it. This makes it more dominant. I would have to guess that it is heating deposits on the bottom of the tank and causing a "popping" sound. This is caused by debris being "boiled" on the bottom of the tank. As the debris gets heated, the sound lessens. Good luck and reply back with any other questions.

I sure hope that you removed that plug from the T&P valve as soon as you noticed it made no difference.

NEVER plug the outlet of a Temperature & Pressure relief valve. It is an extremely dangerous action.

Your rumbling is most likely caused by a fairly large amount of sediment in the bottom of the tank. It needs to be flushed as soon as possible. Don't be too surprised if your tank develops a leak soon after the flushing, it is not a result of the flushing but a result of NOT flushing. The sediment has insulated the tank allowing the metal under the sediment to become overheated by the flame. Also, the sediment provides a dandy spot for corrosion to do its dirty work from the inside.

With proper flushing a tank may last many years beyond its expected life, without flushing it may not last a year if you have a heavy concentration of minerals in your water.

Thanks for very quick answer, both of replies.
It's very hard to describe noise.
It sounds more like a rush of bubbles, then trickles down to get quieter. All takes place in about five seconds, but can be heard anywhere in the house. The closer you are the worse it sounds. My house is 2000 sq. ft. plus full basement. The house and water heater is fourteen years old.
It happens when the clothes washer starts to fill or rinse.
At first it sounds more like water hammer, or pipes banging. Not pipes banging.
I've stood right next to water heater when it happens.
Is it possible sediment is blocking incoming water?
And of course I only left plug in for a few minutes. Thanks for asking though.

At 14 years old, I think its time to start looking at a replacement. I am at a loss as to what the noise would be.

The poster may have hit on something: Maybe the demand from the washing machine is pulling a vacuum on the water heater because the incoming water supply (line?) is not allowing water in as fast as what the static pressure plus gravity (washer inlet lines lower than top of water heater) is deliverying at first...and the cold water to the water heater is not being replenished at that initial draw-rate by the washer. The reasion the noise happens at first is that this is when the static pressure would be the greatest. Then when the washer begins to fill, the pressure in the tank is reduced.

I don't know for sure either...but we are all trying our luck at theories.

You might see how fast water comes out of your water heater drain valve at the bottom. Word of caution though: Be prepared when you open it that it may not seal 100% after you shut it off, if this valve has never been opened. If it keeps dripping out the drain hole you may have to go out and buy a brass female thread (hose-thread) cap cover with rubber washer inside.