You might consider upgrading, as there have been a few "High CPU" fixes since 10.1.6 was released.
Here is one that may apply to you.
RTVSCAN uses 100% of CPU for 5-60 minutes
Fix ID: 1879071
Symptom: Rtvscan.exe may consume 100% of available CPU for a period of 5-60 minutes. The issue is intermittent.
Solution: Rtvscan.exe was modified to prevent a case where the IDB processing logic could get into a loop, consuming all
http://www.symantec.com/business/support/index?page=content&id=TECH101820&actp=search&viewlocale=en_US&searchid=1299165071839
Password recovery for Symantec Endpoint Protection and Symantec AntiVirus
http://www.symantec.com/business/support/index?page=content&id=TECH97006&actp=search&viewlocale=en_US&searchid=1299165359803
I am moving this post to the Endpoint Protection forum.
Best,
Thomas