Laid down some guitar tracks last night, for the first time since updating to the latest version of Sonar.  I'm noticing a weird playback effect on the recorded tracks, which I would describe as random Tape Flutter or wobble.  Never had this before.  Kind of sounds like the effect you get when you apply audiosnap, or melodyne's offline render, while editing audio, except in this case, it's happening to everything that's being recorded.  I actually went back and re-recorded that parts a couple times, but the effect remained.  Is this something in the latest update?  It's really a subtle effect, but very noticeable on my guitar tracks.

First I would double check your preferences  and audio settings are correct. 
Use a higher buffer setting to track. 
Shut off background processes like the internet. If windows 10 is updating while your recording this is not good. 
Check your interface by recording to a different DAW or a free wave editor. 

Also check for 'Remove DC Offset' being enabled in Preferences > Audio > Playback and Recording. This causes distortion when recording mono inputs.

I have gone through my preferences/settings.  I actually disabled the DC Offset option previously, to resolve a different issue that I was having (can't remember what it was).  The first thing that I tried when I noticed the flutter, was turning DC Offset on again, but it didn't seem to make a difference.  
 
This effect doesn't seem to be related to buffer settings.  At the moment at least, I'm not having any signs of low buffer settings.  I have my ASIO set at 512ms.  I usually keep it there for mixing audio, and I'll lower it to 192ms for recording midi tracks.  FWIW, I do record everything at 96k/24bit. 

So I guess you're probably direct-monitoring the analog input through the interface while recording; is that right? If you monitor through SONAR do you get the same distortion of the live input, or only on playback of the recording?

Yes.  This is correct.  I record my guitar tracks through the S/pdif connection of my Kemper Profiler.  Sounds fine when monitoring live.   I do have "Use ASIO Direct Monitoring"  checked in my interface settings.  I also notice that the "Input Echo" button is usually lit when tracking in Sonar.  Not Sure if this matters.
 
I'll give your theory a try tonight and report back.
 

brundlefly
So I guess you're probably direct-monitoring the analog input through the interface while recording; is that right? If you monitor through SONAR do you get the same distortion of the live input, or only on playback of the recording?

Are you rendering mp3s or wavs?
Are you using fast bounce?
Have you tried listening on multiple playback devices?
My car sometimes creates an almost leslie-like effect on an entire mix, but it also does it to music that i listen to from Spotify and whatnot.  It may be an artifact of bluetooth?

Is the clock source for your S/pdif connection stable?

Is it some weird phasing thing going on? Where are the outputs/sends of your guitar tracks going? 

If you are both monitoring the audio directly theough your interface or from the Kemper and you have "input echo" turned on on the track then you'll be hearing the guitar twice. Once through the interface/Kemper then again when Sonar echoes it back to the interface some milliseconds later.

Depending on the latency setting the returning echo from Sonar might sound a bit like doubling, odd phasing which will reinforce some frequencies and weaken others or as a slap-back delay.

It shouldn't affect the recorded audio though, unless the echo from the track is then somehow being returned to the track that's recording so you are recording both the guitar signal from the Kemper and the delayed inout echo from Sonar. If that's happening then a phasing problem that sounds thin and a bit warbly might well be the result.

Might be worth checking your signal routing to make sure that isn't the case.