Unrecognised system process saturating CPU
This was indeed down to some structure being left over from a SQL2012 AV group as had been doing some testing on these servers during a period when they were not in production as they were the only hardware in different DC's suitable.

During the next window of opportunity I rebooted the servers and the performance of both servers has vastly improved and the processes are no longer appearing. (added to my list of issues to all the ones Brent details on his website with SQL2012 AV group issues)

2012 AlwaysON Setup

A must read for anyone attempting to configure these. As noted in Brent's articles I found a number of pitfalls, more tricky than expected and currently have decided to postpone the rollout due to my own issues with unsuccessful multisubnet failover (i could only get this to work in 1 direction) and above mentioned performance overhead.