After a lot of troubleshooting I’ve finally found a component that was causing continued high CPU.
This issue has been happening on a system that has had Windows 7, Windows 8, Windows 8.1 and Windows 10 on it. The majority of the time KIS (Kaspersky Internet Security) was well behaved. Going into Windows 8.1, and recently Windows 10, has seen an almost constant 15% of CPU use. Fully wiping the system and re-installing Windows has not resolved the problem and with KIS being the very first product installed on a pristine Windows 10 install I am confident that there are no product conflicts introduced by me.
TL;DR ? Turn off Mail Anti-Virus.
After disabling this option…
It’s pretty reproducible for me and the KIS product is fully updated as of the time of posting this.