Fan sensor failure in syslog

Hi all,

the Server is flooding my syslog with messages:

Fan sensor detected a failure value
Sensor location: Hard Drive Fan 1 (sometimes number 2 or 3 are shown)
Chassis location: Main System Chassis
Previous state was: OK (Normal)
Fan sensor value (in RPM): 12728 (different values between 1230 and 53210)
Event-ID: 1104

and:

Redundancy lost
Redundancy unit: System Cooling Unit
Chassis location: Main System Chassis
Previous redundancy state was: Lost
Number of devices required for full redundancy: 5
Event-ID: 1306

But after 2 minutes everything's returned to normal with event-ID 1102!
The Message Cycle returns every 3 minutes, is wrong with it? The system runs stable and the temperature is normal@26°C.

In the DELL Doc's I've read about to replace the fan, but it's running all ok!
First time the failure aprears was after a automatic server restart. Another restart didn't fix the problem. :-(

System: DELL PowerEdge 4400, Windows 2k Server

THX4help

Greetings
monty292