If the portable has a gain control bring the gain way down till the noise is way down and move around The noise should start coming up as you get close to the source.
If the portable has a gain control bring the gain way down till the noise is way down and move around The noise should start coming up as you get close to the source.
I keep my 2 feet on the ground, and my head in the twilight zone.
I had trouble like that back in the 1980's with a strong loud intermittent buzzing when I was on 75 meter Am Phone. It was most noticeable on 75 and particularly when the receiver was wide open on AM. it would come and go, on for a few minutes, off for a minute, on for two minutes off for 5 minutes, but on wet rainy days it was absent. Eventually tracked it down to a leaky insulator on a power pole about 2 blocks away.
I keep my 2 feet on the ground, and my head in the twilight zone.