[Elecraft] Horizontal Chaff in P3 Waterfall and Brief K3 "Deafness"

[Paul (N1HEL)]

I'm a new K3/P3/KPA user and contester (about 6 mos.), and I encountered some weirdness I can't explain during this weekend's 10m contest (where I operated all-CW).

Things started out with the gear operating just fine, as usual.  As the contest wore on (late on Saturday and after about 1/2 way through Sunday), while I was running stations and I would often see bright, multicolored (mostly green/blue) horizontal lenses of interference-like graphics on my P3-SVGA waterfall (spaced perhaps a vertical inch apart) while I was transmitting.  This was accompanied by occasional loud static-like pops or "snaps," and sometimes such a "snap" would cause the K3 to "go deaf" (not receive) for a second (or two), causing me, for example, not to hear the last part of my own CQ call in the monitor, or the first part of a station's response.  I don't recall having this problem while running in S&P mode in this contest.  

I was running the N3FJP 10m software, which keyed the K3 through a USB/Serial line (with a PigKnob in the loop).  My antenna is a Spiderbeam, up 30 feet, about 100' distant from the RV that serves as my shack.

Since the symptoms seemed to get worse as operating time built up, I thought it might be heat-related.  My setup has the K3 at desk level, the P3 on top of it, and the KPA on a shelf just above the two (as shown on my QRZ.com page).  But none of them seemed hot (with the KPA just a bit warm to the touch).

I was doing probably a 60-70% duty cycle while I was running stations.

I did not see these symptoms in the SSB or CW Sweeps, or in the ARRL SSBWW contest recently, but I believe this time out, I was getting better at running stations, and drove the equipment harder (KPA at a full 500w) and more continuously (600 Qs over the two days).  I don't believe my equipment config changed much between contests, except for moving my mic around, exposing more mic cable.

Any ideas about what my problem might be?

Thanks for any suggestions,
   
  -Paul, N1HEL