degraded staus message during post

replaced both hard drives and rebuilt the raid 1 configuration. everything worked fine for about a week and now the same thing. Is something causing the machine to eat hard drives?
during the boot post screen says the system status is degraded but boot able. I am running a raid config with two WD hard drives and win 7 for my OS . curious if one of the drives may be bad or what else would be causing the degraded message. the machine works fine after it finishes booting up.
Any thoughts anyone??