Stuttering, popping and crackling upon audio playback

First, a little back story: for quite a while I was having issues with CPU spikes when working with MIDI (Kontakt 5, Engine, etc.). There was a very interesting and useful thread that had a solution. The solution was to go into Sonar's preferences, set "Enable Set Threaded Ideal Processor" to false, and adjust the "Mix Thread Count" number until the problem went away.. Setting the Mix Thread Count to four seemed to get rid of the CPU spikes on core one and distributed the workload across all of my cores. 

However, just yesterday I was working on a track that only contained five audio tracks and four buses. Each track had two instances of Slate VMR, and each of the buses had one instance of VMR, Relab LX480, and Slate VTM. Simply playing back the audio would give me quite frequent stuttering, pops and crackles. I decided to try a few more adjustment of the Mix Thread Count. Finally, setting that number to 6 fixed my problem. That's it. One moment I have horrible noise upon playback of audio. I changed that one setting from four to six and the problem goes away completely. 

My question is this: why am I having these issues? Why don't the default settings in Sonar seem to be compatible with my computer all of a sudden (I've been using Sonar X3 and now Platinum on my current laptop for over three years now without these issues, which have started in the past couple of months)? 

promidi
Could be many things.  As a starting point, are you using the latest drivers for the PreSonus AudioBox USB Interface? Available from here.  http://www.presonus.com/s...downloads/AudioBox-USB

There have been other reports that an enabled wifi card could be the culprit.  

Also , is it plugged directly into a USB port on your PC, not a USB hub? 

Others may offer other possibilities.

Yes, I have the latest AudioBox USB driver installed, and it's plugged directly into my laptop. I disabled my wifi card when I first got the computer because I heard that it could cause issues like this. Still looking for the culprit :(