if you really want to do this then be aware that this will void your warranty.
Both fans suffer from the small physical dimensions, they are 40x40x20 mm only. For decent throughput they have to have high rpms and that makes noise.
here are the specs for the Sunon: http://www.xpcgear.com/40suhispfakd.html
and the YS Tech: http://www.ibfnet.de/pc/643064-fd124010mb-1a5-ekl-kugellagerluefter-ys-tech-fd124010mb-1a5-12-v-40-x-40-x-10-mm.htm
which only is 10 mm thick. Both are rated at 27 dB(A) which surprisingly isn' t that noisy. Both deliver a " tacho signal" (which I can' t translate well now), i.e. a feedback how fast they' re turning.
Replacements should at least deliver the same throughput (in cubic feet per minute, cfm), run on 12 volts, have the same dimensions and offer the feedback signal. I don' t know what your home market is but there should be offerings for this.
In the PC area these tiny fans are used for hard disk enclosures. I researched this topic a while ago and found that fans from Xilence would match. But I never could get a hold on these.
Ede Kernel panic: Aiee, killing interrupt handler!