Hello, Sorry a wall of text but I hope it helps.
First off. This was based on a system using an Nvidia GPU. Intel CPU and multiple sound cards were tested.
The fix for me appears to be Nvidia related. So if your system is AMD GPU based then this probably wont work.
If you arent very tech savvy please dont try this and I take no responsibility if you break things...you know a disclaimer.
This worked for me so I am hoping it will work for more people even though there is a big chance not everyone.
Only thing I noticed was there are still some NPC dialogue missing so I hope/assume this is a different issue.... but for the last few days I have not had a single audio hiss, random sound files playing, missing sound effects etc etc.
Over the last week I have been doing much research in my spare time and trying different things concerning the terrible sound issues that many are experiencing
I am using Windows 10 Pro as well if that matters.
I am using the Nvidia 360.00 drivers. The newest ones made all sorts of things go wrong system wide
So I downgraded to this version.
Anyways, after multiple clean installs of drivers, trying 2 PCI sound cards as well as my on board sound card I may have found a fix.
I read this on some well known tech forums and so I gave it a go, it was not ESO specific but it worked for other people experiencing sound issues and low frame rates in many types of games.
There seems to be a conflict with some of the extra drivers Nvidia installs as a part of their package.
If you go to your control panel>Programs and Features (Or on Win 7 its add remove programs)>Scroll down to where you see all the nvidia drivers that are installed.
There are multiple ones.
Nvidia Graphics Driver (version XXX.XX)
Nvidia Physx System software
Nvidia Gefore Experience
Nvidia High definition audio drivers
Nvidia 3d vision driver
and a few others related to 3d vision and High definition cant remember all the names.
I right clicked and removed anything related to high definitioin audio since I have my own sound card, I removed the 3d vision since I dont have 3d monitor and I removed Geforece experience (Some people may want to keep this but I dont like it and it has issues of its own)
All I had left from Nvidia is the Nvidia Graphics Driver and the Physx driver. DONT DELETE THESE!
After this go into the device manager and under the sound video and game controllers tab you may see 2 or so listings called "High definition audio device" this is the Nvidia HID device that no longer has drivers. Right click them and choose disable.
You may also want to make sure windows is set to not automatically install missing drivers, I always have this turned off. Since I prefer control over what gets installed.
Restart your system.
For the past 3 days since doing this I have had perfect sound on the 64bit client. Where as the last 2 weeks my ears have been getting abused with many random hisses and screeching sounds appearing out of no where.
I hope this can help others like it helped me. A lot better playable experience.