Using an old mac mini as a lossless music server, the noisy fan in my mac mini spoilt my listening. A replacement fan from ifixit was ordered and promptly delivered.
Installation not the easiest job; step by step ifixit guide was easy to follow, informative and very comprehensive. Complete success and our noisy 'ol blighter has been silenced.
If using a mac as a music server, reducing background noise is critical. The hard disk and fan are likely to be the noisiest components in a mac mini- simply replace the fan and install a Solid State Drive. The silence is golden....