I had this problem when i was running sonar on windows 7 but on windows 8 problem solved till yesterday which i update sonar to the latest version.
Here is problem: My PC has 8 cores and in the performance window on sonar it shows 8 cores are running but for some reason the first core is hitting the top and makes some crack and noise when it reach to the red and the rest of the cores are almost showing 1 or 2 bars. The project i am running is not heavy as the other project i use to work.
Is there anybody here experienced this issue before? 
Thanks