BadCRC Drive Errors on Software RAID1

[Andy <andy@besy.co.uk>]

Hello List,

I am running 2x Seagate 250GB SATA-II 7200.9 disks configured as linux 
software RAID-1.

The following errors occasionally appear in /var/log/kern.log:

  kernel: ata1: translated ATA stat/err 0x51/84 to SCSI
  SK/ASC/ASCQ 0xb/47/00
  kernel: ata1: status=0x51 { DriveReady SeekComplete Error }
  kernel: ata1: error=0x84 { DriveStatusError BadCRC }

I had assumed I have a bad disk, but the odd thing is when I connect 
either disk individually I can use DD to fill it with zeros to its 
capacity without any errors.

Do you think I have a bad disk, or should I suspect a problem with my 
SATA controller or RAID-1 setup?

Thanks, Andy