If I take the headset off, enable the speaker and transmit through the handheld microphone, there's a feedback noise. Any way around this? I've tried turning the volume down but it didn't help much.

Sidetone level is too high

How do achieve the right balance so you hear that with a headset, but don't feedback with a cockpit speaker?

Shouldn't the cockpit speaker have zero sidetone? Sidetone is designed to replace the natural hearing of your own voice that is blocked by the headset, so you shouldn't need it with open ears.

Seems like enabling cabin speaker should shut off sidetone and that is not happening in this case.

Mike C.