Clicking and Popping Problems during playback !

Hi everyone,
I am currently facing clicking and popping, or sounds " zzzz" and "zzz" during playing in my Sonar X2 Producer ! I am using a PC laptop core I 5 with 4 Gb RAM running on windows 7. It is ok during recording as Everything goes smooth. However, after done with recording and jump into mixing. For the vocals track, I added EQ, Compression from Sonitus plugin. And everything seems to hear find. But after adding a plugin " AAY TUBE" or " Waves Art Tube Saturator", clicking and zzzz sounds start right away. I test opening google chrome and open some pages, it went worse. is it because of my computer? I tried to figure out different ways adjusting the recording tabs in preferences. This is what I did, and there is two things I want to ask and need help from you guys: 

1) I went to preference and turn of multiprocessing, then it somehow reduce the clicking, but still exist.

2) I went to the asio panel of my focusrite 2i2 driver and adjust the latency from 0, increasing to higher and higher, even to the highest. Then the problem is gone. ! 

So I am asking if : 1) What is the purposing of turning on the multiprocessing by default. Is there any thing affected if I turned it off ? 
                             2) During recording of course we turn the latency to the lowest to get the direct monitoring, but if we turn it to the higher or the highest during mixing, would the quality of the mix be affected or anything we need to consider? 



Please help me with this problem. Thanks in advance ! 

So I am asking if : 1) What is the purposing of turning on the multiprocessing by default. Is there any thing affected if I turned it off ? 

If you have a multi-core processor leave it on.

2) During recording of course we turn the latency to the lowest to get the direct monitoring, but if we turn it to the higher or the highest during mixing, would the quality of the mix be affected or anything we need to consider?

That is correct. I use a mixer, and monitor via that so I don't even worry about low latency at tracking time. Quality is not affected. Everything is delayed and synced together so you never notice the latency. If however your are monitoring effects etc via Sonar and trying to playback live you will, hence the lower latency needed at tracking time.