are you sure is a valve noise?? or is a piston slap?
Wear or improper adjustment.
The fuel injectors make the ticking noise you hear at startup, especially when the engine is cold (colder temperatures).
does it have a ecotek valve fitted?
The noise after flushing the toilet is typically caused by the water refilling the tank and the valve closing.
Possible causes of furnace blower motor noise during startup could include worn bearings, a loose fan belt, or debris in the motor.
check the cadillidic converter under the car.
first off is the clacking noise when in park as well? if it is it may be a valve tap. you can research a valve tap it is common and usually not a huge problem right away.
There could be several reasons why you have a noisy hydraulic valve lifter. One reason could be worn our parts in the entire valve train. A loose rocker arm could also cause noise.
or it could be worn valve stem seals. which causes a little bit of oil to build up on the valves when you shut the engine off or stopped at idol. this is burnt offon startup or when you takeoff.
Your furnace may make a buzzing noise during startup due to a faulty motor or a loose component. It is important to have a professional inspect and repair the furnace to prevent further damage.
If clicking while trying to start then might be a bad starter. If clicking while running, then might be valve/lifter noise.
a broken rod or valve lifter