Re: Dell XPS 15 9560 Fan Always On and Always Loud
The most reliable solution I've found to quiet the fan is to unplug from AC, suspend or hibernate the laptop, then plug the AC back in and finally 'resume'. If the laptop becomes unplugged and is plugged back in again, the fan will kick back on and you will have to repeat the suspend gimmick. It seems this issue is caused by a BIOS flaw that keeps the CPU in a higher package C state (PC3) than necessary when it detects the AC power. (I've been through each and every BIOS release to test this issue).
So, by 'sneaking' the power in while the laptop is suspended, I've been able to enjoy a CPU/package temperature over 45C without the fan staying on constantly and the package C state reaches the lowest-possible (PC8). The fan will run if the temperature is high, and will turn back off when the temperature drops.
Unfortunately, after suspend, the SMBIOS table becomes corrupt and I'm unable to adjust the thermal profile from 'quiet' to 'performance'. But at least the fan is off! Certainly can't be expected behavior for the little fans to run 100% duty-cycle when plugged in. Good thing is the warranty will be long-since-expired when the fans fail, so you'll be able to justify buying another laptop that doesn't have this issue.