Constant Clicking on 4100

My network had some problems so I shut everything down. When I restarted the 4100 is working fine but there is a constant clicking. There is nor activity showing on the CPU (usage 20% nothing going on) or Network. The drive LED’s are solid blue. If I unplug the ethernet cable from the router the clicking continues. If I reboot the system it reboots fine, stays quiet for a couple of minutes and then goes into clicking mode again. Any help/suggestions welcome - thanks Bob