I am baffled. I've been recently resuming work on various Sonar projects after a recent upgrade to Windows 10. One problematic Sonar project was stuttering (recurrent, random short pauses) during playback, so I finally just opened a blank project and copied and pasted all the tracks to it...presto, it worked! No more pauses during playback. However, after only one session in the newly remade project with no problems, now I'm getting constant crackling during playback. On EVERY project. In Reaper, too! Even online when I'm watching a video in YouTube (I have my 2 RME Multiface II's as my only enabled audio devices). I haven't changed anything, just crackles galore for no apparent reason! Any other similar experiences out there? Thanks!

I would start by checking that all onboard audio is turned off. I wouldn't delete the drivers in hardware drivers manager,  disable anything that isn't the RME. 
If you have different bit rate settings for multiple devices this can cause a problem, so all settings should be the same. 
I can't yet confirm this but it appears that Windows sometimes  resets audio to default settings after an update scan. I'm going by comments I have heard from others who had similar problems.
You may need to increase buffers in audio settings. 
What are your computer specs?

Have you ruled out the possibility of a hardware issue with the interface?
 
I recently had a weird crackle/noise problem with my Presonus Audiobox 22VSL.  When enabling monitoring on an input channel in the DAW software, there would be a flood of horrible distortion noise, which would calm down a bit when I played, but the sounds would fade in and out and have lots of noise associated with it.  I tried upgrading / reinstalling drivers, ensuring Windows was up to date, cold booting the system, tweaking buffer sizes etc. but the problem remained.  It wasn't until I switched the channel I was using to the right input that I realised the issue was with the interface as this channel worked perfectly, and only when going in & out of the DAW software with it; local monitoring on the input sounded fine.
 
Not saying you might be experiencing a similar issue, but it's worth eliminating as a possibility.
 
Is the only ('only') change to your system the Windows 10 upgrade?  Do you have another not Win 10 system you can use to test the interface(s)?

Had also some crackles the last days .
This reminded me to update the video card driver ,
cause this  (not updated) drivers have been the reason a couple of times 
for crackles aso here.
This crackles since updating this drivers are gone  in my box.
Not updated video and chipset driver can be the cause for such issues.
Hope this helps
Pragi
 

Thanks, guys...computer specs:
Six core i7 Gulfport 980 3.3 ghz
16 gigs RAM
1 TB Hard drive
128 gb SSD Audio Drive (28% free)
Windows 10 Home Premium (current on updates)
 
I have everything set at 24/96 kHz. I tried making a new project at 48khz, and added one midi track with a drum sample soft synth, and still the crackles remained.
 
I had no trouble like this before with my Windows 7 and same exact computer and hardware, but like I said two days ago I didn't have the crackles with Windows 10.
 
Thank for the tip about input monitoring, but none of my tracks have that turned on.
 
Like I said, it evens happens when I'm watching a freakin' video on YouTube...lol
 
Maybe I screwed up by actually deleting the Realtec onboard audio driver (which I did about a week ago) and the results of doing that are just now showing up. I will try reinstalling that driver and disabling it as you suggested.
 
Thanks again for your help!

It is really a process of elimination as you know. If you remove drivers completely your motherboard bios is looking for a driver and can't find it. Depending on the setup it might try and go to  a default setting.
I have confirmed that bitrate settings were rolled back in my onboard sound. Not sure if this is your problem...just throwing that out there. In my case the audio engine would stall momentarily.
 
Your interface and specs are pretty good. No reason to think there should be a problem there. If it only happened after the win 10 update then I would suspect this is the issue in some way. Your settings all worked before that. 
 
Elsewhere on this forum, others have found problems with win 10 indexing files and doing updates while trying to record. One good suggestion was to unplug or disable the lan connection while recording.
 
If you have CPU throttling enabled try disabling it. Check your audio buffers.

Thanks, Starise...right, a process of elimination is what I am currently going through. I narrowed it down to my analog summing signal path. When I output a track in Sonar to the Master output and send that output through my first analog out of my main Multiface II, it sounds fine through the Multiface headphones jack. Only when I output each track to separate analog outputs of my two Multiface II's that go through daisy chained Black Lion PM8's into a separate interface (a mouthful...lol) do I hear the crackling through my second interface's headphones, and now the crackling has changed its sound somewhat, now sounding more like a plain ol' (but huge) nasty distortion.
 
So my next step will be to reroute the summed stereo signal into my only two open inputs in my main Multiface II and see how it sounds going to that instead. I work two jobs, so I will have to wait until tonight to try this. But yeah, what a mess...and again, just started happening for no apparent reason!! I'll keep you updated... 

I should mention that even just one track alone soloed has the horrible distortion through my current analog summing path. Bizarre.