I've connect a servo motor to raspberry. I have too an speaker connect via audio jack 3.5 mm. When I use gpio pwm it produces interference with speaker and it begins to make annoying noise. When I did "gpio in", stopped it.
I think that like both works with frecuency mHz it makes interference, but its impossible that the pulse output be only on the pin? and do not make interference with the output audio? If I have pwm mode, and play music, servo motor gets crazy turning around.