NT4.0 Problems

Hi,
I have a windowsnt4.0 Data Base server.
Every once in a while the drives flash and grind and the system becomes extremely slugish and after approx 5-10 mins the system becomes normal.The drives are a raid 5.Nobody is running anything big to slow the system down,it just seems to take this pattern and become normal again.We have other servers on the network and have no problems. Has anybody enountered this problem and can it have something to do w/maybe the raid 5(bad drive)
Thank You