That rumbling sound from the water heater
If you've started noticing a low rumble or popping sound coming from the water heater, usually right when the burner kicks on, you're not imagining it. It's not the house settling and it's not the pipes. That sound is water trying to boil up through a layer of mineral deposits sitting on the bottom of the tank, and it tends to show up gradually, then one day you actually notice it during a quiet evening.
It often gets dismissed at first because it's intermittent. You hear it for a few seconds, it stops, and life goes on. But if your water heater is more than four or five years old and you're on well water or Nixa's municipal supply, which pulls from a mix of groundwater sources with a fair amount of hardness, this is worth paying attention to now rather than later.
Why this is common in homes around Nixa
Water in this part of southwest Missouri tends to run hard. Minerals, mostly calcium and magnesium, come out of solution when water gets heated and settle to the bottom of the tank as sediment. Over time that layer hardens into something closer to a thin crust than loose grit. The burner underneath has to heat through that crust to reach the water above it, and the trapped water underneath turns to steam, pushes up through the sediment, and makes that rumbling or crackling noise people describe as the tank 'boiling.'
Houses in Nixa run the gamut from older ranch homes built in the 70s and 80s with original or aging plumbing, to newer builds out toward the edges of town that still have hard well or municipal water running through them regardless of how new the house is. Age of the house doesn't protect you from this. Age of the water heater and the hardness of the water are what matter.
More on this from Reading List The Rumble That Means The Burner Is Heating Through Minerals.
What you can check yourself
Start by looking at the tank's age. Most water heaters have a serial number on the manufacturer's sticker that encodes the production date, usually the first two digits or letters. If the unit is pushing eight to ten years old and you're hearing that rumble, sediment buildup is the most likely explanation.
You can also do a simple flush yourself if you're comfortable with it. Turn off the power or gas to the unit, connect a hose to the drain valve near the bottom, and run water out until it looks clear instead of cloudy or gritty. If a lot of grit or flaky material comes out, that confirms what you're hearing. Doing this once a year, especially given how hard the water tends to be here, cuts down on both the noise and the strain on the burner.
Pay attention to how hot the water gets and how long it takes. Sediment acts like insulation between the burner and the water, so a tank working harder than it used to, or taking longer to deliver hot water, is telling you the same story the noise is.
When it's time to call someone
A flush that won't run clear, or a drain valve that's clogged or won't open at all, usually means the sediment has built up past what a simple rinse will fix. At that point you're looking at a more thorough cleanout or, if the tank is old enough, weighing repair against replacement.
Rumbling that's gotten louder and more frequent over a short span of weeks, combined with rusty water or a tank that's visibly aged, is a sign the inside of the tank may be corroding along with the sediment problem. That's not a do-it-yourself fix. A cracked or failing tank, especially one under pressure from a hardened mineral layer, can fail suddenly rather than gradually, and nobody wants that happening in a utility closet next to drywall and flooring.
If you've flushed the tank, confirmed the age, and the noise persists or gets worse, it's worth having someone look at the burner assembly and tank condition directly rather than guessing. Given how common hard water is throughout this area, a lot of local homes end up needing this kind of once-a-year attention just to keep water heaters running their expected lifespan instead of failing early.