suddenly started getting fan speed errors

hi,

I run 6.2.4 on RNDU4000, and suddenly started getting errors in log and email:


Thu Jun 11 2015 9:24:08	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).
Thu Jun 11 2015 9:22:11	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (711 rpm).
Thu Jun 11 2015 9:19:54	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (711 rpm).
Thu Jun 11 2015 9:16:02	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (711 rpm).
Thu Jun 11 2015 9:14:36	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (710 rpm).
Thu Jun 11 2015 9:08:54	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (711 rpm).
Thu Jun 11 2015 9:07:23	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).
Thu Jun 11 2015 9:06:16	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).
Thu Jun 11 2015 9:04:15	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (708 rpm).
Thu Jun 11 2015 9:03:33	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (711 rpm).
Thu Jun 11 2015 9:02:27	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (707 rpm).
Thu Jun 11 2015 9:00:56	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).
Thu Jun 11 2015 8:58:54	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).
Thu Jun 11 2015 8:58:18	
System: Fan 'Fan' in enclosure 'Internal' speed is below threshold. (709 rpm).