[Elecraft] Strange noise on 20m with no antenna

[Julian, G4ILO]

While tuning around the 14.100 region with my K2 connected to the 
transverter but with the transverter switched off (therefore effectively 
into a dummy load) I noticed a strange noise around 14.130. It's a sort of 
hash, rather like atmospheric noise, about 10KHz wide but peaking in 
strength at that frequency. Whilst listening, it suddenly stopped and 
changed to a squealing noise, like RF oscillation.

I've heard similar noises from switched mode power supplies, but it's 
usually radiated so you need an antenna connected to hear them. I cut the 
power to everything here anyway, and it didn't seem to make a difference.

With everything disconnected from the K2, running off its internal battery, 
I can't hear the noise, so I'm not convinced that this is being generated 
inside the K2. As I reconnect the power lead, computer cable, antennas etc, 
the noise starts to be heard, but the thing that brings it up the most is 
when I plug something into the key jack.

Normal band noise (from the transverter, or the HF antenna when connected, 
drowns this noise, so it has probably been present for a long time. But I 
have no idea what it is or where it is coming from. Anyone had anything 
similar to this, and found the answer?

73,
--
Julian, G4ILO. (RSGB, ARRL, G-QRP, K2 #392)
G4ILO's Shack: http://www.qsl.net/g4ilo