You did not mention the milage again, yet you said after the first oil change in your post first after what? Buying the car? Or engine change?
Here lies the mystery behind the noise.
How long did the car drive after the last oil change?
Actually the New oil serves its time In two different stages.
First stage is cleaning up the deposited gunk inside your engine with added detergents in your new oil.
Second stage is sealing the metal inside your engine with anti wear lubricants.
If you have changed the oil too soon that means you are over cleaning your engine and you didn't let the sealant interval of the oil start.
You surely have changes the oil too soon as you said it drives hardly 100kms per week. That too not. On Highway. Your cars running is low and your oil hardly gets time to treat your engine.
What I would suggest is an 8k oil change. Run your oil for 8k. And then change it. This will go with time as your oil gets old.
It's still in cleaning process.
We came with this issue back in 2014 with an idsi city with a member.
Xulfiqar bhau was kind enough to shed light on this mystery and get. Us out of our misery. Refer to that post. Of you may.