[Elecraft] Vibration noise from KPA500

[Dave]

Hello,

I have a KPA500, (working fine), however, at one, and only one, fan 
speed there is a resonant vibration coming out of the amp.  It is one 
speed above just starting...

It is also clearly a resonance vibration, not a PS hum.  It is also only 
present when the fan goes up one speed from whatever is the first speed.

Has anyone else experienced this, and if so, what was the fix?

-- 
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources