I'm hearing an S9 "click" at just about
once per second, everywhere on 20meters
where there's not a powerful station's
signal. It clicks for maybe 3-5 seconds
then stops for a few seconds. Not always
symmetrical (3 sec noise ~ 10 sec no noise).

Click sounds like what I'd imagine a charging
and regularly discharging capacitor might do.

Freq independant, it's everywhere on the 20m phone segment.



Do you live on the country side? Could it be a farmer's electric fence? If
not that how about the ignition system on a gas central heating system

73
Jeff