UPDATE: Michael Aaron Murphy, a System 76 Engineer reached out on Twitter and shared a link to this issue on their Github. This fan noise issue is known and they are working on a solution. You can see the Twitter comment here and the Github activity here. I am happy to hear they are working on it and appreciate their continued willingness to openly engage with the community.
I’ve had a System 76 Thelio for a little over four months now and a consistent issue that I’ve been experiencing is persistent fan noise even when the machine is idle. After a few measurements the idle decibels of the fan noise were in the mid forties to low fifties at idle. As a podcast host (Coder Radio) and generally someone who finds fan noise incredibly annoying, that decibel level was not tolerable. This issue is also particularly grating given how much work went into the design of the case and the general aesthetic of the Thelio that makes you want to actually have it right next to you on your desk but is undercut by the loud fans. For some perspective, under the “silent” setting in the BIOS the fans were still hitting decibel levels in the high forties
Like every good nerd, I turned to Reddit and Google to find out if other people were having similar issues and sure enough they were. The Thelio has a special custom board (referred to as the daughter board) that runs a lot of the internal processes with an eye toward avoiding proprietary technology. Among other components the CPU fan is wired through the daughter board which then connects to the motherboard; it’s difficult to see at this angle but the daughter board is on the bottom of the 2.5″ hard-drive enclosures on the upper right of the case.
In terms of fans, we have an intake fan at the bottom of the case that pulls air (hopefully cool air) into the unit from the outside and a large CPU fan on the upper left of the case. 
One small oddity I noticed was that my Radeon GPU’s fans were actually pointing toward the intake fan. That seems to suggest that when the GPU fans spin up they are actually pushing air against the flow of the intake fan. I need to do a little more digging on this aspect of the air flow to see what is actually going on airflow-wise. Either way, I am pretty sure that the GPU fans facing the intake fan is not really the cause of the noise issue; in fact, I was able to confirm that the noise was the CPU fan by just listening to where the noise was coming from relative to the locations of each individual component. System 76 has made the Thelio to be user-accessible and that came in handy here; it was really nice to have hand screws instead of having to dig out tiny screwdrivers as one has to do for Apple and other machines. Unfortunately, due to the size of the GPU, I did have to remove it during the modification process to get easy access to the daughter board.
The process itself is simple — just rewire the CPU fan directly to the motherboard, then change the CPU fan settings to manual and modify the PWM chart to your tastes; I was pretty aggressive in terms of turning the fan all the way down and again I do not recommend this. A key piece here is that there is more than one fan in your machine. Even if you don’t have a GPU in your Thelio there’s still a bottom intake fan. I chose not to rewire or modify that one out of concern for the long-term health of the machine, but it’s definitely possible to do so for the brave of heart. You can see the cable coming from the CPU fan to the motherboard directly in an image to the right; I strongly recommend using the built-in cable management slots to make sure that you don’t have it just dangling there. Once you’ve exited the BIOS and saved your settings you’ll notice that on boot the fan kicks up as it always has but then cranks right down. I saw a noticeable reduction after making this change.
Before this process the fan noise was audible in a simple audacity recording, but in this recording taken after it is not:
Assuming my Thelio doesn’t melt (half-kidding) this modification is well worth it to me.
It’s up to you if you want to make this modification but I’m disappointed it’s necessary. Thelio is a premium product with a premium price tag and in most cases it lives up to that. However, that’s all undercut by what seems like an issue that should’ve never made it past QC. Coder Radio listeners know (and some have griped) that I have a soft spot for System 76 and it’s true. I’ve met some of them. I like them on a personal level. I admire their mission. I know they are talented people. I want them to do well. Unfortunately, I believe that many commentators in the space and I, let our admiration of the mission of Thelio affect our reviews of Thelio, giving it just a bit too much slack. The thing that made me realize this is that I am preparing to do some coverage of the upcoming Mac Pro and comparable pre-installed Linux machines for Linux switchers from macOS from a developer perspective. I realized that if the Mac Pro had anywhere near this type of fan noise issue, I would pan it out of hand in the harshest terms possible. If we Linux switchers are going to be serious in our conviction that Linux is better for developers than macOS, then we have to be intellectually honest and not grade on a curve. The closest correlated Apple option should be the yardstick by which we should measure any upcoming Linux development machine from any vendor. My hope for System 76 and the other Linux vendors is that they step up to the metaphorical plate and knock it out of the park. Let me know what you think on Twitter!
