Do all AIO coolers come with crappy noisy fans? Seems a bit ridiculous to pay £100 for a cooler then need to change the fans.
Pretty much. It isn't really their fault though. If they included silent fans then they'd get far worse performance than all of the competitors, which would show in reviews - then nobody would buy them.
There isn't really a standard when it comes to noise. For a lot of people, the AIOs only ramp up the fans under load/gaming, so if they've got headphones on anyway, it may not make a difference to them.
Also, to create higher static pressure, the fans need to run at high speeds to generate the forces, which obviously creates more noise.
With custom watercooling, we normally say adding more rads allows us to run our fans at lower speeds. Obviously with AIOs this isn't possible as the small 240/120mm rads are pretty much running at their full potential. When 360mm AIOs come out properly, or thicker 240mms, we may start to see lower fan speeds from the manu's fans, but it'll most likely take a long time to run through.
To answer the OP's question though, Swiftech Helix 140s are meant to be good. Also BGears B-Blaster 140s (although they're hard to find in the UK).