Steam Extreme CPU Usage While Downloading Games

I've recently fresh installed Ubuntu on my laptop (specs below, but more than enough to work with) and started downloading one game on Steam, but suddenly I start feeling my computer a lot slower than usual. I open System Monitor to see what's causing the problem and see that Steam is using practically all the CPU available, I pause the download and see the CPU usage is still high.
I've been testing distributions for the last 10 days and always see performance problems with Steam and its games.
Edit 1: I restarted my laptop to apply some system updates, however the problem still persists.

Edit 2: I also have problems running the games I downloaded on Steam. I usually have 120 fps for 2 minutes and then the games get to slow and lock on 10 fps.

The specifications of my laptop:

My laptop starts running all cores at 100% when downloading. This could not be a "feature" of the Steam client. Is more like an "active wait loop bug".

Well, the workaround is as easy as renice the steam process.

This is what I did:

for i in $(ps aux | grep steam | awk '{print $2;}'); do renice -n 19 $i; done;

With this change, this CPU goes down and the CPU fan also, but the download and disk write speeds are similar.

Ok. You can also use the "cpulimit" tool instead and set the max cpu rate, for a "bad" process as Steam is.

Basically, when you have a bad neightbour process, talk to the OS to restrict that behaviour.