[Freeswitch-dev] Openzap Fxo pre-answer

I have an fxo port with an incoming call, somewhere when the call is being routed to the destination a pre-answer is happening and taking the FXO off-hook and playing ringback to the FXO caller. This causes billing to start on the incoming call, is there a way to prevent the FXO being taken off hook during pre-answer, is this because the FXO port is generating audio packets? Thanks, Simon