I've recently experimented with the load external mp3 function, and found that:

a) if you load one mp3 into a sound object, then issue the load command again, for the same object with a new mp3, the time elapsed attribute of the sound object is cumulative.

b) working this way with several large (80-100mb) mp3 files, the processor spikes to 100% capacity and memory usage by explorer shoots through the roof

have you tried destroying the sound object to halt the download?