[Elecraft] K2 Problem

[w2bvh]

I've got a problem with my K2 and would like some advice. S/N is around 
1500, and I built it in mid 1999. No problems with it since.

The problem started with a complaint from a nearby (8 miles away) ham. 
He was seeing regularly spaced spurs across his passband when I 
transmitted FT8 (with a XV50 - 6 Meter transverter). I double checked 
his complaint with a friend who is around 35 miles away. He saw the same 
thing but the offending signal (of course) were much weaker.

I did a LOT of debugging of the system, assuming ground loop(s) were 
causing the problem. I actually found and fixed some problems with 
ground, but there are still spurs.

Recently I decided to stop focusing on ground and just simplify my 
setup, which is quite complex (2 IF rigs, 7 transverters and multiple 
power amps). Box by box, I disconnected things until I was left with 
just the K2, a straight key and a dummy load. The spurs are still there. 
Even the transverter is not connected. And to make sure that grounding 
is not an issue, I powered the K2 for awhile off a battery. Probably 
more interesting, the spurs are there even when the K2 is set for CW!

With the K2 set to CW and 28.100 MHz, the significant spurs are (with 
respect to the carrier):

+558Hz -39.2 dB

+296Hz -36.7 dB

+178Hz -25.6 dB

-178Hz -25.5 dB

-306Hz -39.0 dB

-558Hz -40.0 dB

I also ran the K2 set for SSB  with a 2-tone generator into the mic port 
and the IMD looks fine .. around -29.5 dB). But those same spurs are 
present on either side of both tones. (I  didn't take actual 
measurements but by eyeball it  looks like the same pattern as with CW). 
I have no doubt these levels are strong enough to cause mischief on FT8.

The measurements were done with an HP8566, in good working condition, 
and I trust it.

I can't imagine this is "normal" for the K2.

I left some phonemail at Elecraft asking for a callback a few days ago 
so I could discuss this, and I'm sure I'll hear back from them some time 
soon. (In this age of pandemics, I have no doubt they're overwhelmed).

But in the interim, is there anyone who's a real expert on the K2 who 
would know a) how abnormal is this? b) what might be the cause?  I don't 
think I'll  fixing  this myself unless some expert says something to the 
effect of "Oh yeah, I saw that a few times, its usually caused by X". 
Hopefully that's what will happen and I'll just fix "X".

Thanks in advance for any help.

73 & stay safe,

--Lenny W2BVH