Ok Peter, the same thing happens to me but in my Bitx40.
When I gently touch the pcb and the components near the AF ic with a stick, I hear the friction on the loudspeaker as a result of microphony.
This occurs even when the Bitx40 receives perfectly.
When the signals coming out through the loudspeaker are loud they distort and I am beginning to think that it is because of this microphonic effect, which is fed back by the sound of the loudspeaker.
I replaced the Lm386 without a positive result.