noisy water heater

Hi all,
We have a 75 gallon, 75,100 BTU natural gas water (State Industries, "Select" model) that probably is seven years old. I routinely drain water off the bottom valve to flush out any sediment.
Lately I have noticed that when burner is on, it "clunks" and "knocks" noticeably (a louder version of what a tea kettle sounds like on the stove).
I assume that it is water boiling near the flames, but thought it might be due to excessive calcium build-up at the bottom of the tank, "insulating" the bottom of the tank from the heat.
Anyway, is noticeable "knocking" when the burner is on an indication of pending failure, or is there anything else I should in response to these symptoms. Thank you.
Best,
doug
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

yeah crud buildup at bottom of tank, it decreases efficency and slows water heating a little. but the tank may run for years like this. i wouldnt worry about it, its no biggie. the noise can get very loud,
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.