Could be a bad ground in your PC or Home
 
GCFI Receptacle Tester
 

unclewall
I just got my NU last weekend and just installed  0.2.1.2 and I have the same background sound that acts just as you describe, I Had a Asus stx II before this card which when installed in the same slot was very very quiet 
I also have a problem with the load, default, apply and save buttons they do nothing at and the EQ presets don't seem to work right  
Other than that its working well

Load, Default, and Apply do nothing in the NU Audio Software, since all changes are made in real-time (except for a couple settings that have a small delay, intentionally).  It shares the UI skin with our Precision X1 and Unleash RGB software.

No issues with ground, my house is brand new, custom, and my studio is 8 feet from the main panel, my PC is on a dedicated circuit as well, and I also use high end power filtration / suppression equipment in my studio for everything.  There is zero issues with interference, ground, etc.  The audio hiss/hum comes on Digital AND RCA outputs, it does not appear to be present on the headphone jack.
 
Yes my speaker cables are fine, the digital output goes 5 feet to one amp, the RCA's go 3 feet to a different amp so I can flip between speaker sets/amps as needed for my environment.  The speakers are in fixed locations and too haven't changed.  I run plenty of my other gear through them with zero noise/issues. 
 
Again, my card was perfect, nothing in my environment changed except the driver/firmware update and now I want to throw the card out the window.  

try to check the ground loop issue it might be the problem it can be easily fixed

Its not a ground loop the op said it occurred on SPDIF.
He also said using a web browser changed the sound and only started when using the updated driver

Load, Default, and Apply do nothing in the NU Audio Software, since all changes are made in real-time (except for a couple settings that have a small delay, intentionally).  It shares the UI skin with our Precision X1 and Unleash RGB software.
 
I've been wondering about this ever since I got my card.  This is just dumb.  Please hide controls that don't do anything.

in my case the screeching noise on headphones/line out starts when I boot up frostbite engine based games after the new driver updated the card to 0.30 firmware, so it stayed even after I rolled back the drivers. Hence the question above - whether the sound described came from the speakers or the hiss is electric from the card itself. On a side note, does anyone know if firmware can be manually rolled back?

I think new firmware might be causing issues

If you were able to downgrade the firmware and the driver, and the problem persists, is it possible the most recent firmware damaged the hardware? I don't mean to induce unnecessary fear, but I think the question is worth asking. it's a genuine question — I have no idea myself. Also, does the problem persist if you fully power off the system instead of just rebooting?

I can confirm I have had the same problem with 2 different EVGA Nu cards in 3 different PCs. Updating the firmware and the drivers made it worse. While troubleshooting the second card I've tried rolling back drivers 3 or 4 versions but with no luck. After trying different combinations of drivers/firmware I noticed the buzzing lessen in frequency but the sound started clipping in and out periodically (like it was losing connection or something). After one final night of particularly exhausting troubleshooting, now there's no sound from any of the outputs.
 
The buzzing/hissing/static noise seemed to happen when playing graphically intensive games. When I play Overwatch it's fine, when I play Apex it buzzes intermittently, but when I play Monster Hunter it only doesn't buzz when I'm in the loading screens (3440x1440p monitor). FWIW, I read one review where the reviewer that had the same problem.
 
I spoke with someone at EVGA and he came to the conclusion that it's some type of interference from my GPUs or PSU. I had the same problem in a 9900k/1080 ti/Gigabyte build, a 3770k/1080 ti/Asus build, and now in my new 3800X/5700 XT/Asrock build (with two different EVGA Nu cards). The only common link between them all was my Corsair AX1200. Admittedly that is an aged PSU with many hours on it, but PSUs degrade very little over time and I'll be darned if I'm going to replace a $350 PSU and $100+ in custom sleeved cables that are perfectly fine when I could spend less on an alternative sound solution. I'll sell the Nu card as-is and swap to an external DAC/AMP combo like the Sennheiser GSX 1200, Schitt Modi/Magni combo stack, or a JDS Labs Element (I or II). This would give my 5700 XT more room to breath considering my mATX board has only 1 free PCI-e slot for the sound card directly under the GPU. Plus overall heat reduction because that Nu card gets TOASTY.
 
Anyway, sorry to hear you're having trouble. I've been reading a lot about this issue and I've exhausted every avenue I could in troubleshooting it since I purchased the first card last November. When this card works the sound is INCREDIBLE. It destroys anything my old Creative Sound Blaster Z could ever do. But it doesn't work and has never worked reliably for me so it's time to move on.
 
Nice try, EVGA. I hope you can figure this out because the Nu sound card is freaking amazing sounding. Unfortunately, the reliability is dumpster worthy.
 
TL;DR
Had buzzing noise in 3 different PCs with 2 different Nu cards. Only common part was a Corsair AX1200 PSU. PSU interference? Idk. Replacing sound card for external DAC/AMP combo. Too many hours on phone with support and digging through online forums to care anymore. Hope EVGA can fix it bc this card sounds great.