Strap a microphone on.
Really you won't hear anything interesting with a microphone right under the four fans.
Look at youtube and find a video of a P2 with gopro and the audio recorded by the gopro should cure you.
I tried an experiment, hanging a Tascam DR-05 off the controller. It picked up good quality sound, which I synced to the video in post-processing, but the P3 doesn't have to be very far away before the sound drops off in volume considerably. It's a weird effect when your point of view is with the craft, but your point of hearing isn't. I'll stick with music!
Depends what you want to hear, the best solution is to have a portable recorder and microphone at the place that is emitting the sound. So..if you are recording video of a wedding for example, have the recorder on the groom himself and sync in post production.
Saw some great online vids from older P2's with GoPro at a monster truck rally in Florida. They had a great soundtrack of the roaring trucks and people talking & cheering.
Turns out they had someone on the ground walking around with a digital recorder getting lots of soundtrack samples then added it in in post. As they do in real movies.