What SAN are you using ?
SAN performance can be very poor but in these cases the CPU will be low (page reads of around 10ms/page) as the server will be waiting on IO.
The fact you've got high CPU usage is very odd and would imply that you're not doing any IO ?
How many processes are running when the CPU hits 100% ?
Can you run sysmon ?
Have any config setting changed ?
If the SAN is the only change (but check what config had before) then it could be that the server is thrashing around looking for IO and not finding any.