if CPU usage jumps up to 33% with constant rate ...it does mean hidden applications are running behind the scene ...
try using selective start ...
step-1
a) Press the Windows + R key on the keyboard.
b) In the Run window type MSCONFIG and click OK.
c) On the General tab, click to select the option Selective startup, and then click to clear the option Load startup items check box.
d) On the Services tab, click to select the Hide all Microsoft services check box, and then click Disable all.
e) On the Start Up tab, click Open Task Manager. In the Task Manager window under startup tab, right click on each startup item which are enabled and select Disable.
f) Click OK, and then click Restart.
Step 2: Enable half of the services
a. Follow steps 1a and 1b to start the System Configuration utility.
b. Click the Services tab, and then click to select the Hide all Microsoft services check box.
c. Click to select half of the check boxes in the Service list.
d. Click OK, and then click Restart.