[Elecraft] KPA500 - fan noise

[Bill]

Interesting post from Wayne regarding the low fan noise from the 
KPA1500. So, I have to ask about fan noise and the KPA500.

Background: I run my KPA500 all the time - my K3 is a 500 Watt XCVR. 
 From time to time, in particular during AM operation, the fan comes on 
and moves right on up in the noise department. Enough, that I have 
considered changing the location of the amp or redesigning my desk and 
putting a door across the shelf the amp lives on (open to the back and 
lots of room of course).

Question: Has anyone successfully reduced the fan noise of the KPA500 by 
fan replacement? If so, please tell me what you did.

Thanks, Bill W2BLC K-Line