go into your NCP and go to manage 3d settings then profile for STALKER and change these settings under power management to prefer maximum performance that will stop the downclocking then you may want to use EVGA  precision to set target frame rate at 60 and see if that helps limit the coil whine.

if you have set all of your games profiles power management to prefer maximum performance in the Nvidia control panel and its still downclocking its sounds like to me your card is not being given a workout so its downlocks to just what it needs to run the game but even then I find that 550MHz way to low to run any newer game the only other thing I can tell you is try another set of drivers it maybe a simple as that.
 
 you may want to check the Power options your using for your pc that should be set to high performance to that one is in your computers control panel that can sometimes lead to a problem like this because the pc is wanting to save power.
 
also you may want to ask one of the EVGA guys if their is a bio's update for your card that fix's something like this.
 
will in a games menu some of them you can push 2000FPS or more anytime you go that high alot of crazy things happen I've never played STALKER so I don't know if they cap the frames in the menu or not I remember I use to play one game that I was getting over 8000fps in the menu and my temps would go throw the roof like watching a F1 car go from 0 to 100.

It's not clocked down to 500MHz since so I wonder if it was just STALKER and the crazy FPS that made the card have a tantrum? The noise was brutal lol

I tried a bit of overclocking today, got it up from 1070 to about 1180 core but got a crash in Crysis 3, lowered it down to 1150MHz and played about 2 hours of Assetto Corsa (quite a demanding racing SIM - 90% GPU load) and it clocked back down to 1070MHz without crashing. This card just seems to love clocking itself down without crashing, it's crashed once and given me the recovered display driver message and that's cus I was a spanner and overclocked it too high without over volting. 

I checked the power profile and in windows it is 'Balanced', if I put it to 'Performance' my CPU frequency is pretty much maxed all the time and I'm not really liking that, in games I've asked nVidia Control Panel to give performance in games though.

What would be a good additional voltage value to maintain say 1150MHz+?