cubase crackles tsk-tsk sounds

hi guys ! nice being here first time
so the big idea is once in cubase,monitors on, and making more then 2 channels and hit the play-
these tsk tsk are taking place. i switched to headphones, the sound is fine ,
but when i switch to the monitors its making these sounds.
on youTube however, my monitors working great as well.
i have:cubase 7.5
soundcard microbook 2 , MOTU company,
monitors company is pioneer.
do you have any idea how to fix it ?
my pc is 8 gig ram. does it have any influence or its something else?

Hi and welcome,

Increase the Buffer Size of your Audio Device, please.