R440 FAN error when adding second CPU

PROBLEM SOLVED MYSELF.

Took a fan from another server and installed. Now no error.

I am glad to hear that issue is fixed. Fan 6 is required when you have 2 CPU installed on R440. Please refer below link for more details

https://qrl.dell.com/Files/en-us/Html/Manuals/R440/Cooling%20fans=GUID-29070724-EBBD-40BD-8D79-00E7BA18B5C3=3=en-us=.html 

Ditto. My single CPU R440 does not include Fan 6. I too upgraded to dual CPU and problem is as OP described. Initially, I dismissed the critical error "Fan 6A is either removed, incorrectly installed, or not present." from the iDRAC9 dashboard because I just presumed the loud fan noise was caused by me installing, at the same time, a Mellanox 10G NIC. Which the system detected as "3rd Party Card" and LFM Mode set to Automatic (changing this to Disabled silences the fans).

Curiously, the other R440 system I took the fan out of (now short a fan) is loud. So if a fan went bad or missing then it will be loud (with fans running at maximum speed).

Hi,

Yeah, Poweredge fans will spin higher when there is a fan issue, either missing or faulty. It is the server's redundancy capability to sustain cooling in the chassis till the error has been addressed.