Does this sound like the dreaded knock oh so many NCs fall t

[Zdos123]

Hello,
For the past 3 months now i've been having a very concerning rattle on mostly cold startups (sometimes after heavy driving if i restart the engine after 5 minutes it does it but much quieter and shorter) but never during actual driving, i've covered about 3000 miles in that time and revved the absolute balls off it (whilst warm) and it hasn't change drastically, maybe a smidge worse.

I thought it could be a timing chain tensioner but my mechanic after listening to a video of it said he thought main bearings or rod bearings, but some people on the euro owners group say tensioners, some say rod bearings, some don't hear anything wrong, i'm completly at a loss.

I went back to the dealer i bought it from (as in the UK you are legally entitled to a 6 month warranty) and they eventually acknowledged it but said they wouldn't repair it as it wasn't likely to fail soon, they said potentially timing chain tensioner. I called them out saying they have to repair it and they are ignoring all my emails and phone calls so whatever it turns out to be i'm going to have to take them to small claims court to pay for it.

This is my one and only car to get me to university and work, i really need to get some second opinions on what it could possibly be and if i'm best off just selling it to a big company with the problem and just letting them deal with it.

I have a few video clips below.

https://streamable.com/htjgsn

https://streamable.com/f8zef8

I will be so incredible greatful for any of you wonderful peoples help/suggestions, it's causing such a great deal of stress and anguish.
Thanks,
Zdos123

Edit : I've tried different oil filters, going from cheap chinese filter to mann helped but going to mazda made no difference. The noise also compleltly dissapears if i crank the engine before starting.