A common cause is frequent replication schedules.  It's not so much as the array is busy handling IOs locally, those are prioritized.   I would adjust the schedule and stagger multiple ones to see if that helps.   Having more replicas than expected isn't a bad thing.  
Anyone know what causes this error?  Opened ticket today; --- WARNING event from storage array PS6100XV repeated 3 times subsystem: MgmtExec    event: 8.3.45      time: Mon Sep 23 01:50:00 2013   Schedule NIGHTLY failed to delete the oldest replica according to the max-keep limit. Proceeding to create a new replica.
Failed to delete the oldest replica email error