Before I start: there is obviously no denying that I'm a no-lifer. I spend all of my free time doing things on my computer and there are no non-computer activities that I find interesting. So it's probably obvious that my computer is extremely important to me.
And now it seems that I'm getting paranoid.
Every time I launch my computer, I fear that something wrong is going to happen, like a long "beeep" and my computer not launching because something inside it just broke. I listen to how it works and I keep telling myself "this is NOT the way it should sound... or is it?". Every time I happen to hear something that I find even remotely suspicious, I instantly take off my headphones and start listening, only to learn that my computer isn't making any unusual noises and it was simply just ANOTHER sound from the outside. Whenever I smell something that makes me think of something burning, I instantly go "OH MY GOD MY PC IS BURNING" and go check the temperature of the components, only to see that there is nothing out of ordinary in there and the source of the scent must be completely different.
On occasion, completely randomly, my computer makes a rhythmic "tok tok" sound, as if something inside it was bumping the case. I have no freaking idea what it is, and it drives me nuts, because every time I hear it, I go on full alert, expecting something very wrong to happen any moment, only to see that computer continues to work normally, with no parts of it going into dangerous temperatures or anything. I can never expect when it's going to occur; sometimes it happens just once during a regular full day session, sometimes I can go days without hearing it, and a few days ago it kept happening with very short delays (below a minute sometimes); when it happened, I was on the verge of my nerves, being all like "OHNOMYPCISGOINGTODIEPLEASEHELPMYPCISDYINGOHGODOHGODPLEASENO". I turned it off, cleaned the fan from dust, and then it seemed to work just fine. Yet I still heard that "tok tok" once the same day... and it was the last time I heard it so far.
Any ideas what it was? Or any other suggestions? (Other than "get a life" of course.)