Okay, frustrating issue here. I was working on a project yesterday and everything was perfectly smooth. I just opened the exact same project now and I'm getting a ton of crackles and pops during playback. Seriously now. How can it work just fine one day and have this issue the next when absolutely nothing has changed since then? Any ideas? Thank you!

Update:
Here's what I've confirmed. It's not related to the mouse. It was just coincidence that the crackling was happening as I was moving the mouse around. I am connected to the internet but there's not update pending or anything like that. I turned off my wireless mouse completely and it was still occurring. It seems to get worse the longer the audio is playing. It doesn't happen at all if I'm just playing back MIDI. The crackling is not part of the audio recording (like a bad recording or anything). It only happens in Sonar. I played back audio on iTunes, on Youtube, etc. and there was no issue. Also, I just opened some other projects and the issue seems to be isolated to just this one project. What in the world does that mean!?

Just for reference, my audio interface is set to 44.1kHz and 512 Buffer Size. 

Please continue to help me trouble shoot. It's driving me insane. Thanks! :)

Is your computer connected to the internet?
Have you had any Microsoft updates recently?
Has your computer been automaticaly restarted after upgrades?

As you mention mouse, a couple things to check. First is the mouse wireless? If so, check batteries and possible interference (any Wi-Fi devices that didn't exist yesterday?). The second is sort of funny, but has bitten me... if using an optical mouse, first flip it over and blow the dust out of the lens cavity, then gently clean the lens with isopropyl alcohol and Q-tip (if necessary).
 
I have had dust get into that lens and it actually triggers a "read" on it, which is flaky and persistent. It affects scrolling speed, mouse interaction and the whole nine yards. The one that got me the most was a cat hair actually got into that cavity.

The crackling and noises while moving a mouse around is common and you can ignore it as it will not have any effect on your recordings. It possibly a wireless or pour shielding of your USB system. I get it and have determined that it's my USB system and there's not much I can do about it other than somehow shield the internal wiring. It goes away if I use a hardwired mouse and keyboard but the wireless is just more convenient as I often move away from the desk while overdubbing vocals and guitar. 
On some systems it's been reported as video card related. 
But bottom line is it does not get recorded. 
To test insert a audio track and set it to record with nothing plugged in to your interface. 
Crank up the gain too. Record this silence while moving the mouse all over and even clicking buttons in Sonar an my guess is the sound will not be recorded to the track. 

Thank you for your responses. I'm still hunting down this issue. 

Here's what I've confirmed. It's not related to the mouse. It was just coincidence that the crackling was happening as I was moving the mouse around. I am connected to the internet but there's not update pending or anything like that. I turned off my wireless mouse completely and it was still occurring. It seems to get worse the longer the audio is playing. It doesn't happen at all if I'm just playing back MIDI. The crackling is not part of the audio recording (like a bad recording or anything). It only happens in Sonar. I played back audio on iTunes, on Youtube, etc. and there was no issue. Also, I just opened some other projects and the issue seems to be isolated to just this one project. What in the world does that mean!?

Just for reference, my audio interface is set to 44.1kHz and 512 Buffer Size. 

Please continue to help me trouble shoot. It's driving me insane. Thanks! :)

Well that is different than the mouse issue.
Could be audio driver related so make sure your up to date with driver and firm ware. 
I've also heard of a static build up being a plug in that goes weird in memory. What does your memory usage show?   
The usual way to trouble shoot issues like this is start disabling Plug ins.  
Also check your cables, including USB,  you never know, I think this just happened in another thread. 
 
I swapped out my USB cable to my interface for one with a Choke on it and it made a difference with the mouse issue. 
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Are you using that midi instrument in your other tunes that work? 

Check the Motherboard manual, and see what slots share with what...if you can move the video card off of any slots which have on board controllers, and such, or reduce the amount of things on or shared on one slot, by moving a card, might help make the mouse on wi fi better, if wi fi/blue tooth devices are interacting with video/audio? , and or video is some how being shared with audio....HDMI audio?.... is not a good idea if using DAWs and add on audio devices/plus on board Audio....So home work should reflect in making sure these guide lines are made, to root out setup issues....turning things off in bios that are redundant, so as to free up and make proper slot assignments so less is shared by force....too much shared on one line,or slot with a video or audio card in that slot causes problems!...win may also randumly share when booting up...so one day it is like great, and then on one day, it is not....I found....until you make it so .
 
Regards

Try turning off

64 bit precision engine in Sonar.
Intel speedstep (or amd power now).
Your core parking (google for details).

Make sure you min/Max processor states are set to 100 in control panel

Try updating your audio interface drivers and firmware as well.

in my case, the crackling started the first time I opened x3 after installing platinum.   for all the GUI problems with x3, it had been perfectly solid in the audio field before today.