I have/had a bunch of Gigabyte 750Ti/970/1070/1080Ti cards. The fans on the 970s died within a year and the fans on the 1070s died within 6 months. Meanwhile, I have 750 Ti's with mostly working fans.
All these cards have crappy sleeve bearing fans. Except for the AORUS series, which is the flavor I have my 1080 Ti's in. The AORUS series have double ball bearing fans which are basically what every card should have; they're superior.
I have also contacted Gigabyte, trying to buy replacement stock fans but they do not sell any parts. But they replace it under warranty, but that might take weeks/months depending on your location.
So you can really only get replacement fans on ebay but they will die just as soon as your stock fans did. But if you send the card back for a warranty process and if they notice that you have replaced the fans, your wannanty will be void so in case the card dies, you have to put the original fans back.
In case you're going with ebay fans, you really only should look at how much amps the stock fans pull after checking yourself (for example 970 G1 - 0.20 amps, 1070 G1: 0.35 amps) and use fans that's equal or lower than that value (unless you want to power the fans straight from your PSU or a fan header). Some cards Gigabyte cards have different fans with different amps so better to check all three and most importantly, check the headers and only order what you can plug in without having to cut cables and replace headers.
TL;DR: only buy cards with double ball bearing fans or you're going to have a bad time.
Thanks for the info bathrobehero.
Point taken about the low quality fans.
I stripped the GPU last week for a 2 monthly service and that's when the problem started.
Ill bring an anemometer home from work tomorrow and work out the air flow on 100% fan speed per fan.
Probably 3D print a new cover and slap some decent fans onto the new GPU case and run them direct from the PSU on 100%.
If I have any issues with the GPU not having a feedback tacho pulse, Ill have to throw an Arduino together to send a false PWM signal back at it.
I had to do this with an S7 last year, as I didnt have the right fan and the IO card wouldnt run the miner up without a feedback.
Shouldn't take more than a few hours to do with an oscilloscope.
Im thinking the GPU will probably be a little more lenient as people do water cool these and throw the fans away anyway.
Probably the most important thing on a GPU is the cooling fans, its stupid skimping on the fan quality.
Happy days.