Even people who don't consciously hear the sounds are affected like those who can't tune them out.
This is very true, and several posts have pointed this out before. Ralf, Halcyon and Edward Ng wrote really good posts.
It is normal to be about 20% less effective over long time due to this disturbance, so any sensible company will have desktop or laptop machines that are fairly quiet. It simply costs too much to have people produce 20% less results.
In the same analogy companies put servers in a server room so noise does not matter. This is cheaper than it is to make them quiet.
For private use the connection between time and money is not as clear, but it should still be considered. So assume that you spend 20 hours a week infront of your computer. Lets say you do something usefull half that time. That still means that you gained 2 hours every week by having a silent computer.
Now figure out how much it is worth to spend on silencing that rig to gain 2 hours a week. Can you really afford to run a loud machine?
Still there is some point where the diminishing returns should stop us from silencing the rig, unless silencing has turned into a hobby, like it has for most of us.
As you know anything classified as a hobby does not have to be rational anymore
Wim wrote that he could not find a good looking wallclock that dind't tick.
The simplest trick is to use clock mechanics without seconds. With most mechanics it is just the seconds that tick noticably.
Ofcourse you should keep that nice looking clock that you like.