FIFO hum when run with MPD

[cpyarger]

One of the more interesting methods of using this program would be to have it streaming a FIFO file from MPD. unfortunately when both programs are run at the same time all you get over the FM link is a loud annoying hum.

[Emerica]

Please see - http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
I did not write this code, just made a fork with a couple changes, so it doesn't get lost if the other host goes down etc.

I'm not sure you'll find a good way to do this without a second PI or making a kernel driver as the above link suggests. The gpio pin is getting flipped essentially with timing that works well when the PI's load is very low.
Basically the way its abusing the GPIO is eating away the resources of the PI.
Once you have MPD streaming, it's eating resources that would be modulating the signal and you hear the noise. In very basic terms.
I ran into the same sort of problem trying to do similar with ffmpeg.
If you could make a driver to offload, You might get it done on one PI. Out of my league atm though.
Otherwise, If you could supply the fifo from another machine you might be ok. On Pi converts, One pi modulates.