Fan issues with new motherboard

[bingobongo]

In my quest to resurrect my last Dreamcast I've now got a second problem - or mystery at this point.

I checked all the obvious connections on the old motherboard and still never got it working - so I bit the bullet and bought a new PAL V1 motherboard - exactly the same as the broken one.

I've just finished installing it and it boots up perfectly, complete with French as the default language (I'm not French) - so, all almost perfect - but the one thing that immediately struck me was the tremendous noise/racket coming from the fan. Surely it's not this load normally? I've had one since 2000, I'd never noticed that before. I powered up my Hong Kong NTSC Dreamcast and sure enough, it's silent as hell... just faintly purring in the background. To make a comparison, the loud Dreamcast could (almost) give the XBOX 360 a run for its money - although nothing can ever truly beat that beast of a jet engine -

Ive just done some web searches and immediately it's all "Yeah, it's normally that loud" - and even here in searches before I created this post. Everyone seems to say it makes a racket?

The Hong Kong Dreamcast is a stock console - I'm the only owner and I've never put a Noctua fan in it, or any other fan - just custom shell and GDEmu and bracket kit/Dream PSU

Are we talking two different physical designs? Some loud, some super silent? I am genuinely confused - and pondering getting a Noctua - but how can they be so different? It's like night and day. There were a few very scattered comments saying theirs were also quite silent, I'm guessing like my HK model.