Hello again dear OOF members

It's been a while since I had a chance to read around here, but I've finally had the time to do some hobbies and the engine swap from a X25XE to Y26SE.
The transplant went really well and it was an easy modification to fit everything. The Y26SE I got was in excellent condition, but I have one rather disturbing issue.
The cambelt was changed less than 2000km ago (less than 1250 miles) and it is documented. At first start I had a squeaking sound coming from behind the cambelt cover (confirmed by removing the acc belt). I removed the upper screws of the cover to inspect rotation of all tensioners while a friend manually turned the engine, but everything moves just fine and there's no cambelt wear and tear to be seen. I fired up the engine and let it idle for some time (less than ten minutes) and the sound faded away. Engine running very very smooth

The next day and the engine was cold, I heard the sound again, but not that loud - also faded away after a while.
Any idea what this could be? When turning by hand it sounds like bending a brand new cambelt (the somewhat "crunchy" sound). The squeaking reminds me of rubber against rubber, but not likely a bearing with poor lubrication.
I don't know if the tensioners was changed with the cambelt, but most likely yes since it was done at a dealer (service tag confirming change).
I really should change everything anyway, but I'm hesitant to do that myself as I need all the tools and parts (plus the high possibility of failure). Getting the parts in Norway is really tricky and expensive, and the expertise to change it is a really really rare find.