Hi jlkinaz and welcome to the EVGA forums! When the fan goes to full speed have you tried flipping the eco mode switch to see if this "resets" it to normal speed and does this issue only happen while eco mode is enabled? 

I flipped the switch from Eco On to Off and the fan continued at the same speed - Turbo mode.  Switching back to Eco mode On did not change the fan speed.  The only thing that seems to reset the PSU is a shut down.  Reboot does not reset the fan.
 
I then Shut Down the PC and changed the switch from Eco On to Off and then powered up the PC.  I let it run for a couple hours with Eco Off and it never went into Turbo mode.  I then switched to Eco On and the fan went silent (as it should).  Temperature of PSU (T_Sensor attached) is now at 33 deg C.  I expect it to go into Turbo mode when it hits 35 deg C.  Does any of that detail help?
 
At what temperature should the fan on the PSU engage at full speed vs. normal speed?  If it is not temperature regulated, what triggers the fan to switch to change from one speed to another?

jlkinaz
So, I'm not alone.  Sounds like you have the very same issue.
 

Pretty much. Would be nice to know exactly what the temp set points are for the fan etc. This is the only fan that makes noise on my pc.

It sounds to me like when Eco mode is on and the fan stops, it should slowly ramp up once the temps climb to help bring the temp back down. Which is not the case.

****CRICKETS***** EVGA?

I was just about to post the same issue with my G3 850. I've been using it with ECO off and the fan at low speed isn't that bad. I'm still in the testing stages with a brand new GTX 1080 with a Hydro Copper block so I haven't seen the PSU go thru all the stages yet. Out of curiosity I turned on ECO and the fan went silent as it should. Then after maybe an hour of near idle use, browsing, the fan kicked up to a higher speed. I assumed it was the middle speed and it was very noticeable. So I waited and waited but the fan never kicked down again. I let the PC run idle overnight and the fan was still at the higher speed in the morning.
 
I shutdown, turned the ECO off, rebooted and the fan was again at slow (quiet) speed. So it appears the G3 850 does not kick the fan back down once it cools as described. At idle I am pulling 170kw according to my backup power supply and about 400kw running the Heaven benchmark. I decided to buy a PSU about double the size required to future-proof the headroom. Also, when I researched the EVGA ECO mode I thought the extra size "might" be able to keep the fan off even under moderate loads. After a little testing it seems with ECO off the 850w will continue to run the fan on low speed without needing more cooling. But with ECO on the extra headroom of the 850 still can't run silently for long under even light loads.
 
But I have no idea how long the fan will need to run at a higher speed with ECO off because it never slows down after it hits the mark to ramp up. So far, I haven't gotten the 850 to ramp up the fan with ECO off to know if it will slow back down on it's own. But it's definitely not slowing the fan down once it ramps up with ECO on. I will try to keep loading it with ECO off to see if I can ramp up the fan and then see if it will slow down when cooled. 
 
It would be nice to know if this is a random thing or all 850's have this issue because I bought this from Micro Center and can make a simple exchange within 30 days. I went with the EVGA 850 because it was on sale for the same price as the 750.

zerocool101
My G3 850 PSU does the samething. Randomly turns up the FAN RPMs even when not gaming. Very annoying.

The issue isn't that it turns the fan on or speeds up... it's that it doesn't ever slow it back down, it just stays on high speed.
 
The fan is supposed to turn on at 50C, which isn't too difficult to reach. But it's supposed to stop again when it cools down to 40C. That's the issue in this thread.

The fan behavior that has been described in this thread is normal for that unit. It is a byproduct of producing a high watt PSU in a smaller chassis. The fan noise is necessary for keeping the internals as cool as possible, failure rates of G3 units are very low as a result. If the aggressive curve when using ECO is too loud, I would recommend running the unit with ECO mode OFF as that tends to have a gentler curve that will ramp up much less under gaming or heavy loads. I use a G3 in my own system and find the ECO OFF fan behavior agreeable. 

I also just upgraded from a G3 650w to a G3 850w
 
The 650w did not have this problem, but the 850W do. The rest of the system is the same, as with the old power supply.