Something I've never noticed before with my KX1 - when an external battery is hooked up, i hear a brief audio blip or beep every 2.5 seconds. I don't recall hearing this before, the only change I've made is putting in lithium internal batteries. Haven't tried pulling them out yet.
Since it only happens with the external battery, suspect the battery - a
battery with significant internal resistance can do that (with any
radio). I suspect that battery is about to have a short lifetime left.
There is also a remote possibility of leaky capacitors in the KX1, but
that should reveal itself n matter what the power source may be - so
since it happens only with the external battery, suspect that external