Constantly hearing a flushing sound from your toilet every 15 minutes can be annoying, as well as a waste of water and money. Even if you do not have plumbing skills, you can perform tests to diagnose the reason for the flushing noise. The toilet may simply require a quick, inexpensive fix using basic tools. If you do need to purchase parts to fix your toilet, you can find them at a hardware store or home improvement center.
Remove the top of the toilet tank.
Check if the chain connected to the flapper in the tank fell off the flush arm. Sometimes, the chain falls off and gets trapped under the flapper, which does not allow the toilet tank to fill properly. Reattach the chain to the flush arm by placing the hook at the end of the chain through one of the holes in the flush arm. The chain should have a bit of slack, but not so much that the excess gets trapped under the flapper when you flush the toilet.
Check the water level in the toilet tank. When the water level is set too high, water spills over the vertical overflow tube and prevents the intake valve in the tank from shutting off properly. Adjust the water level by turning an adjustment mechanism at the bottom of the toilet tank, or turning a screw at the top of the toilet's intake valve. Flush the toilet to verify that the water level stops below the top of the overflow tube.
Replace the flapper. An old or malfunctioning flapper can cause a gradual loss of water in the toilet tank, which causes the intake valve to cycle periodically. This cycle may have a flushing sound. To determine if the flapper is to blame, pour a couple drops of food coloring into the water in the toilet tank -- just enough to color the water. Refrain from using the toilet, and check the toilet after 45 minutes to see if the water in the bowl is colored. If so, you must replace the flapper valve.
Replace the contents within the toilet tank with a tank kit. Take care to purchase a tank kit that matches the type of toilet you have. Follow the manufacturer's step-by-step instructions to replace the contents inside the tank.