I've been putting together fanless PCs for my own use for a few years now, also disliking the aircraft-taking-off sound of many desktop PCs when they are switched on. I started with the Zalman Reserator[0] water cooling tower, then moved to the Zalman TNN 500-AF[1] where the case was a giant heatsink (it was an amazing piece of kit), although more recently have been using ready-made fanless PCs (which are more widespread now most of the components run much cooler). The site at http://www.silentpcreview.com/ used to have useful information for people building quiet PCs, and https://www.quietpc.com/ still has some good components (and ready-made machines) too.