Why Platinum's CPU meters activated w/noise

How are you making the noise? If you are using a plugin in Sonar, or actively recording and playing it back via input echo on a Sonar track, then Sonar is active. The Sonar CPU meter, unlike the Windows activity monitor, does not actually measure how active your metered CPU core is. It "displays the time it takes to process a buffer full of audio data as a percentage of the maximum time available to process that data and maintain uninterrupted playback." So if your noise playing is using a Sonar audio buffer it would be expected to be active. 
 

are you actually trying to make said noise, or is it more of a square wave buzz noise that just happens to be in E. I occasionally get a similar sound when everything starts up .plugging unplugging the interface usually fixes it(komplete audio 6)