Abnormal heater sounds are important indicators. Boiling = scale on heater. Ticking = uneven heating. Water-flow sound = air in lines.
See if any of these signs match your device — each one increases the likelihood of this fault.
These are the causes we encounter while repairing Strange noise from water heater — ranked from most to least common.
Limescale buildup on heater element
Scale chunks floating in tank
Air in hot water line
Loose pressure relief valve
High water pressure on heater
Metal expansion with heat
Any of the following = a danger signal — call now and don't try to fix it yourself.
On-site diagnosis, clear pricing before any work, and a documented 6-month warranty.