[Elecraft] KPA500 Running Hot?

[N4CW at aol.com]

When I operated the OL-OK RTTY DX contest, I ran the KPA at 300 Watts  
output. The fan would generally
go up three steps when I was running 'em, and the temperature got into the  
60's. The fan was a little loud, but tolerable with earphones on. But 
today, I  had occasion to need the amp to complete a QSO with a DX station on 20. 
I ran  150 Watts output and my transmissions were no more than 3 minutes 
long. Yet,  every time I was transmitting a minute or so, the fan would kick 
in, and it  stepped up three or four times by the time I was finsished. Now 
THAT was loud!  Plus, the top rear of the amp was quite warm. Exhaust from 
the fan was warm,  too!
 
I didn't have the presence of mind to check the temperature today.
 
Any ideas? Has anybody else had this experience?
 
Bert, N4CW