Clipping in Average Performance Load

Hi ,

I use cubase 7.5 as my DAW .
I have editted audio ( Vox ) and had splitted the audio by by bar to sync in proper tempo .

Whenever I play the audio back , I can see that there is a clipping in the erage Performance Load and " click" sound occurs at a few places .

Why does this happen ?
Is there a way to reduce the performance load ?

My System configuration is :

i7 3rd gen processor
1 TB hard disk
Windows 7 64 bit
DAW used : Cubase 7.5 64 bit
Kontakt 64 bit
Audio interface : Focusrite Scarlett 2i4