Audio Devices Becoming Busy

[The All Mighty TCL]

Hey all.
I've an sound card that uses the snd_es137x module and am running FreeBSD5.1R
Every once in a while XMMS stops playing songs saying there is a problem and 
in the console I get:
oss_open(): Failed to open audio device (/dev/dsp): Device busy
This happens on random times, sometimes XMMS start working again after a few 
minutes and sometimes it sticks like that till I reboot.
I'm not using any other programs that use the sound card AFAIK
Does anyone has a clue about this thing?

Thanks ahead.