A good feature gone bad.
According to reports, some are experiencing some high CPU utilization after installing the Windows 10 upgrade. A thread on Reddit, shows that many are experiencing this problem, which causes a laptop fan to spin constantly. If you're a Surface Pro 3 user, you've experienced fan noise before and know how annoying this can be. Additionally, if the fan is constantly spinning, it also means there's a chance that equipment is heating up – which is never a good thing for prolonged periods.
The Reddit thread also contains a fix. The fix is simple but is in an unlikely area.
Tap or click the Notification Center icon in the Windows 10 system tray and tap or click All Settings.
Tap or click the System icon (for display, notification, apps, power – and other things)
Go to Notifications & Actions and deselect the "Show me tips about Windows" option.
Your CPU utilization should be back to normal.
I'm sure Microsoft is aware of this and is working on a fix.