[Elecraft] [K3] Raspy tone on selected bands

[Jon Iza]

Folks,
my K3 is showing  a weird effect on selected bands, namely 7, 14 and 28
MHz, with no effect on the remaining ones. It shows on the P3 as a waveform
with ragged tops, being 14 Mhz the most deformed.
The effect appeared last weekend, when we were in the middle of a severe
heat wave, which has been replaced by a second one lasting until Monday.
I reviewed the archives and found a comment: restart the rig and reset the
filters by pressing and holding SHIFT, so the filter goes to (--NOR--). I
tried that with no effect.
After more than one hour back and forth, the rig recovered and all was well
for the Marconi Memorial.
While preparing for the upcoming IARU contest, the same problem reappeared
again. I have left the rig turned on a few hours but the no cigar.
Any hints appreciated.
jon, ea2sn / ee2a