CAS server showing increased LDAP latency and CPU

Hi,

Periodically one of our 2010 CAS servers is showing increased LDAP latency and CPU maxing to 100% w3wp.exe.  We are Update Rollup 7 SP2 Exchange 2010.

Average LDAP latency in Perfmon is approx 1'800.  CPU is 90 - 100%.  When it goes down, functionality is restored.  It's not constant but it seems to spike for 1-2 hours at a time.

From a client perspective our mobile devices do not synchronize and the Outlook clients connected to the particular CAS server do not sync either, sending receiving.

Any ideas where to start looking at this one?  From a DC perspective the only change has been an increase in DHCP scopes being added, however Exchange does not directly look-up this DC but it is in the same site.

Thanks, Matt.