Thanks for the tips!
In cmd after typing sfc /scannow I receive a message that states, "You must be an administrator running a console session in order to use the sfc utility. Went to Control Panel-->User Accounts and confirmed that I'm already running as admin. Any work around for this? *EDIT* Found better instructions here
and ran scan successfully, "Windows Resource Protection found corrupt files and successfully repaired them".
In task manager and resource manager it shows the CPU spiking and memory faults at 34 Hard Faults/Sec on Resource manager on something associated with AVG Free. Disabled AVG and no more fault there at least.
Ran some music from the OS HD and no issues that I could produce. Annoyingly, it's an intermittent fault, making it harder to trace. Now to troubleshoot the external HD and USB hub...