Buzzing on APX6000XE speaker mic output

I've got an APX6000XE w/ PMMN4062A speaker mic that I'm trying to stream audio from. When I connect a 3.5mm cable to the plug on the speaker mic, the audio is loud and clear but there is a buzz whenever someone is NOT talking. This only happens when the radio is docked in a charger - if it's running on battery the audio is perfect at all times.



It's been suggested this problem could be because the charger DC output isn't filtered.



Any thoughts? Thanks!

Buzzing on APX6000XE speaker mic output