OK... you have pin2 grounded for no input signal. Now use your scope
and trace backward from the RF output collector... moving back through
the audio chain... noting the origin of the 100Hz oscillation.
Normally those radios have only a single transistor buffer for the
mic... followed by a high power op amp (usually mounted to chassis
wrapper) for the audio. Your signal tracing should take long at all.
Hope that helps.

Changing in VR5 (some related to modulation) remove the noise ,
i put vr5 more near ground.

Noise seems generated from somewhere feedback at hight swr....
regulation of vr5 remove noise but what kind of effect can it have on
modulation (in am all semms right RF evelope in the scope and audio
received from another cb)?

Giulia