I buy a customised white box tower with no OS and the least hardware the whiteboxer will ship. I did this in early 2012 with an Asus motherboard, i7 2600 and as many silent/quiet components (including soundpoofing) as possible. I do think PCs should be decibel rated - there's nothing worse than a noisy PC!
Stuff added in the 3.5 years I've had it: 32GB RAM (109 pounds - bought almost at the bottom of the pricing curve), 128GB SATA 3 SSD, 480GB PCIe SSD, muliple 3TB and 4TB fast HDDs, lowly HD7790 card (I rarely play games), an old combo CD/DVD/HD DVD/Blu Ray drive I keep moving to my latest PC cos it's impossible to get such a combo drive new now, 27" 2560x1440 DGM monitor (same LG panel iMacs use).
Problem is that the tech for my next "twice as good" PC (64GB DDR4 RAM, 8-core CPU, USB 3.1, M.2 SSDs, 8TB HDDs, 30" monitor maybe 4K?) probably needs around 18 months more to mature and come down to sane prices, so I'm going to be not far from 5 years between PC replacements, which is the longest for me to date as far as tower desktops go.