The timing of refill sounds can narrow the conversation without taking the tank apart.
The short answer
Note whether water runs continuously, the tank refills between uses, water reaches the overflow tube, or the handle behaves differently. If an accessible fixture valve is known and operates normally, stopping that toilet can limit waste. Do not force a stuck valve or use a cleaner that obscures tank parts.
What to notice
Listen for the cycle
Record the interval between refill sounds and whether touching the handle changes it. Look for visible water movement in the bowl without adding dye or removing parts. A flapper, fill valve, overflow setting, handle linkage, or another condition may be involved, but a sound by itself does not choose the part.
Check the fixture boundary
Confirm that moisture around the base or supply is not being mistaken for ordinary tank refill. Water on the floor changes the urgency and may involve the connection, tank, bowl, seal, or condensation. Stop using the toilet if flushing adds leakage or if the base is unstable.
Plan repair versus replacement
Ask which component is failing, whether the tank and bowl are otherwise sound, and how a replacement would fit the existing rough-in and supply. Include removal, floor condition, shutoff behavior, testing, and disposal in the scope. Efficiency labels can inform a product choice but do not prove compatibility.
One useful question
Does a running toilet always need replacement?
No. Several repairable components can cause running, and some fixtures have broader condition or compatibility issues. Ask for the observed cause and compare a specific repair with a specific replacement. Avoid choosing solely from water sound or estimated age.