I was in the similar need after I bought new and most powerful laptop that I could afford. It might be more powerful than my previous rack mounted 3U server (which was completely silent BTW.) but new laptop started to annoy me very quickly.
It´s Fujitsu AH532 with Intel quad core CPU running @2.2Ghz, has 12GB RAM and 256GB Samsung SSD. Problem was that it´s fan keeps almost silent until it needs to cool down the CPU and it rises it's speed which causes way too clear noise.
I have replaced ordinary stereos with CD players etc. long time ago and listen all my music from PC. I am also music maker so sound card has always been high quality and non integrated. I don't have any mandatory reason that forces me to get silent PC, does there need to be? I just dislike constant fan noises.
And when I am going to sleep I always listen some ambient at very low volume levels which does not cover that fan noise... Same if I watch some movie / document at night.
So, I had to create solution to this problem. I don't use this laptop as portable, it's permanently in it's place so I was considering some solutions that might be out of the question in topic starter.
1. remove bottom cover -> disconnect fan -> add second bigger (slower and quieter) fan in it's place.
-Problem was how to force airflow to go correct spot? From inside it would be very difficult.
2. Doing same but back words. It would need some kind of adapter to direct airflow from out- to inside, it was solution that I considered very seriously.
It would allow using as big fan as they get, with very slow speed to move enough air to laptops cooler. If that fan would be left always on it wouldn't need to be connected to laptop at all, which makes laptop not to "see" it at all. So it might give some kind of error when powering it up. I guess that is not a big deal and can be ignored easily. Did that with my rack PC.
3. First idea actually I got was to use heat sink paste that's also glue, and connect big enough passive cooler to CPU. In my case it was almost impossible as CPU had heat pipes going to laptops heat sink where the fan was.. there just were no any suitable space to mount that passive cooler.
4. Create big box which works as acoustic silencer and put that laptop there. It keeps it's fan noise inside but if it's big enough it doesn't make machine to get too hot. Especially if silencer box has some bigger, slower and near quiet fans installed.
5. This is what I did: I drilled whole to my wall for cables and put laptop to closet. There was electric socket already. Good point in this solution was that I didn't need to ruin laptops cover.
I used one 5m long USB cable that I already had, directly from laptop to external sound card and 7-port USB hub from closet to studio room, to which I connected mouse, keyboard etc. I had also long display cable at hand so I didn't need to buy anything for this.
Closet's door does not even need to be closed and it reduced noise to nonexistent levels.. Ah, sweet silence!