Generically, a very thick oil like 20w50 could be responsible for loud valve train noise (ticking) at startup. An old engine with an unknown service history could also be due for a valve job - adjusting the clearances on all the valves to factory spec so they don't tick as loudly. Ticking noises could also be coming from noisy injectors.
Specifically, it does seem like there are people who run 20w50 or similar in their 4g15. For other readers, note that this engine design is actually a fair bit older than year 2000. There is an enthusiast group in Trinidad and Tobago who seem to like 20w50 and 15w40 for this engine, Link here if you are interested. From reading their forums and some mitsubishi forums, it sounds like this is indeed a very noisy engine under normal circumstances. Yours could be operating normally, with correct oil.
If the noise does not worsen or continue longer over time, I would say this is a non-issue. If the situation deteriorates, it could become a critical issue, and one of the above is likely the cause.
I was not able to find a de facto oil weight requirement for this vehicle. I read everything from 5w30 to SAE50.