My diagnosis for what it's worth:
If the cam chain tensioner is hydraulic (does anyone know?), then it makes perfect sense that hot starts will cause a clatter. The same thing happens on my Hyundai car with hydraulic tappets.
The tensioner creates tension when there is oil pressure. I am presuming that the oil enters the tensioner under pressure (it will be a low psi) as soon as the motor is started. When the engine stops, oil drains from the tensioner and tension is lost.
When the engine is hot and the oil is very fluid, it will drain almost immediately from the tensioner and thus the noise will occur on a restart. Colder less viscous oil, would remain in the tensioner and keep the tension for the next start. So there would be no noise on a cold start (or the oil has drained from the upper cylinder head into the tensioner).
The valves on my Hyundai sound terrible from a hot start but as soon as pressure builds up, the noise goes away.
It's also possible that there should be some sort of one way valve that acts to retain the oil in the tensioner when the motor isn't running and that this is the component that has failed. I would need to see a tensioner to determine how they work.(anyone got a workshop manual?).
It is also possible that the oil put into the bike from the factory, has properties that prevents this draining of the tensioner when the motor isn't running.
I too, noticed that this noise started immediately after the first service and the oil was changed.
In any cause, I am not concerned that this is a failure or that the bike is about to expire. Anyone who has owned any air cooled Suzukis in the past, will know that cam shaft knock and clutch rattle were all part of the experience of owning a Suzuki and add to their character.
These motors are unbreakable.
I would however suggest, when starting the bike, that you allow the oil pressure to rise and the noise to abate, before you set off or rev the bike. Hardly an issue.
Now if it was a Honda and you heard this noise ....