A pipe hums. But the sound of the pipe groaning is caused by the toilet ballcock. This leaky toilet is costing you money. It’s easy to fix.
The humming is from the toilet ballcock. The ballcock is the tall mechanism on the left side of the toilet tank. When water leaks out of the tank a drop at a time, the ballcock will fill very slowly. When the tank is slightly low on water, the ballcock will barely be on and it can vibrate like a saxophone.
Check the water level in the tank and see if it is up to the top of the overflow tube. If the water is up to the top of the overflow tube, you should put a repair kit in the ballcock. The price of a kit and the installation is cheaper and easier than changing the ballcock. Before shopping for parts, get the name and model of the ballcock or bring the top assembly with you.
If the water level is below the top of the overflow tube, put some drops of food coloring in the tank. Wait 15 minutes and see if any colorant appears in the toilet bowl.
If you get colorant in the bowl, change the flush valve seal. A flush valve seal could be a flapper, a tank-ball on a rod, or a seal connected to a flush mechanism. Flappers and tank-balls are fairly common, but there are many models that require a unique part so bring the old one with you when you go for a replacement.
Don’t replace it with a complete-repair-kit with below quality parts at premium prices. Remove the old parts, take them to a qualified plumbing supplier, and it’s done in one trip.