Clicking (maybe knocking) Water Heater during use

Hello everyone, I'm in need of some professional advice. We have a water heater, it's:
- Not new, about 4 years old - Electric (two heating elements) - Big enough for our 4 member family, so it's not a mini model - Located in the garage - NOT connected to a water softener (we live in indiana, really hard water here, it's on our list of things to buy) - Been drained once in the last three months to replace a bad element, but no solvents/vinegar used to dissolve calcium or anything
Recently I heard a sound coming from the water heater DURING USE, perhaps from near the top. It's not as violent as a knock may sound, but I don't know how to tell the difference between a knock and a click! So it's one of the two. The sound does not seem to happen after use, only during.
Any suggestions? I'm thinking of draining the tank tonight by turning off power, cutting cold water supply, opening a hot water tap while connecting a hose to the bottom valve of the water heater, then after the pressure is gone opening the value to drain the liquid & loose calcium deposits. But do you think this will help?
Any suggestions are much appreciated, thanks!
brad
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In my experience you have calcium build up in your tank. My old tank did the same. I went to drain it and found it would not drain. I replaced it and found the tank 1/4 full of calcium. This water heater was part of a home I just purchased. Draining is a good idea. It might help some. Guessing here you do not flush the tank regularly.
If it drains slowly, even with the temp/pressure valve open. There could be a lot of calcium buildup. Might be time to run it into the dirt and be thinking of a new one some day
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On 24 Aug 2005 08:32:58 -0700, snipped-for-privacy@hotmail.com wrote:

It sounds like you have a well. Wells can have water that has gasses in the water, which when heated causes hot water faucets to expel air when first turned on. Those gasses can also cause noise when the water is being heated. As others said, Calcium buildups can cause it too, but the gasses are another possibility. I never quite understood how those gasses get in the water, but I think it has something to do with the type of water and minerals. I learned this reading some websites that discuss "well problems". A google search for those words might get you this info.
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As you drain out the hot water, cold water is replacing it. You can get some noise from the expansion/contraction that takes place as well as the two waters mixing.
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