Dr.Doofy
Brief follow-up to this issue, in case it happens to anyone else, all six cards were in fact faulty and required RMA/replacements.  There was apparently a batch of cards, sourced through Amazon in my case, that had this particular fan issue.

Did you finally found a good unit without this problem?

Having this same problem with a set of 1080 SC cards. RMA is the only option here?
 
Edit: Purchased from Newegg.

RMA seems to be the way most of us are going. I am hearing that some people are having success when they install a hybrid kit, but I can't verify that for sure.

I was hearing the fan speed changes during gaming so I tested mine with GPU-Z using the render test to stress the card.  Guess what? My Step-up GTX 1080 GAMING ACX 3.0 has the same problem described in this thread.  I submitted my data to EVGA support and am now happily waiting on my replacement card.  No fuss no muss, EVGA is still the best, period.  
 
PS.
This is NOT a driver issue.  I tried two different versions of the driver being sure to scour the system in safe mode using DDU after each, no change.  The problem is with the card, I just hope the replacement works as it should.  I don't like taking my system apart to install / de-install cards as this can lead to problems caused by dust migration into connectors, connectors becoming loose, accidental ESD, etc...

Buddy of mine has had 3 in a row with the same issue, They are now sending him a 4th.

I am sure he will eventually comment on his experience with the issue.

That's the problem with the SC/FTW's their on custom PCB's by the vendor. Fan controller could be bad on PCB. Glad I bought a reference design card, I've had 0 issues with mine.

Just received my new RMA for this very issue and it does the exact same thing.  I will have to live it since EVGA clearly has an issue here they need to work on and I don't want to go through another RMA.

Same issue here with three cards in a row.  I have never bought anything other than an evga nvidia gpu but guess I am about to.
I love evga and their customer support but if they cannot make a card that runs correctly...

EVGA is looking into this issue. They've stopped RMAs on 1080s with fan speed fluctuation problems until they figure something out.
 
It's hopefully something wrong that can be fixed with a VBIOS update.

arestavo
EVGA is looking into this issue. They've stopped RMAs on 1080s with fan speed fluctuation problems until they figure something out.
 
It's hopefully something wrong that can be fixed with a VBIOS update.

i just read this and i just submitted a ticket about the rpm issue, hopefully i dont have to send mine back in then if thats the case cause i sure like this one :)