RAID 1 problem on XPS GEN 4 System

Purchased machine new in 2005.  From 2008 on I've had intermittend problems with the RAID controller.  When I boot the system the RAID information screen shows everything is fine..normal, both drives recognized.  After the machine boots I get a message saying a drive is missing (always the mirror...thankfully) and I should replace it.  When the machine was under warrenty,  I would call DELL, a tech would look at my system and confirm the drive was missing and dispatch a technician who would replace the "bad" drive and I would be up and running.  The mirrored drive would be rebuilt and the system would work for a while...sometimes 3 -6 months, sometimes less.  Recently the problem has become much worse.  About every 5 times I boot the system the mirror drive disappears, I reboot the system...it finds it but says the array is degraded and after the system is up and running the drive is rebuilt...takes 2-3 hours.  I don't believe it's the drive because A) I only use this system once or twice a week and the current mirrored drive (they're both WD...same size) and B) it always shows up when I reboot.  I'm thinking the problem is with the INTEL 82801FR SATA Controller (driver 4.5.0.6515 version A07) or perhaps with the motherboard.  Any help would be appreciated.  I'm going to include some of the error messages I get when this occurs.  Thanks.

Array 0
Status: No active migration(s)
Write Cache Enabled: Yes
Size: 465.7 GB
Free Space: 0 GB
Number of Hard Drives: 2
Hard Drive Member 1: WDC WD2500JD-75HBB0
Hard Drive Member 2: Missing hard drive
Number of Volumes: 1
Volume Member 1: ARRAY
 
Volume 0
Status: Degraded
System Volume: Yes
Write Cache Enabled: Yes
RAID Level: RAID 1 (mirroring)
Size: 232.8 GB
Number of Hard Drives: 2
Hard Drive Member 1: WDC WD2500JD-75HBB0
Hard Drive Member 2: Missing hard drive
Parent Array: Array 0

Found 1 Event(s)

Event 0
Time Stamp: 0x1C8E28CE2B2AE1E
Function Code of Request: 0xFF
Unsuccessful Retries: 0
Error Code: 0x2
Additional User Info: 0x1