Audio works, then stops then works again

Hi all
Quick question if i may, this is really baffling me. I have onboard sound on my xfx 750i mobo. ( realtek, i believe) i have installed the latest drivers and for some reason i have this strange problem. If i have my speakers plugged in the back of the PC. the sound is really good. Good quality, then for some reason the audio will cut out then after a few seconds it will come back on. No matter what im listening too, music, watching a film etc... allways does it. Theres no pattern to it, i can listen to a whole song with out pause, then the next song will do it throughout. Also im my gaming (CSS) the audio is nowhere near as good as what it was in vista/xp, i cant hear as much as what i used to be able too, yet when i listen to music, when its not cutting out the quality is fantastic.
I tried my headphones in the front socket, now if i use my headphones the sound does not cut out, however regulary it seems that sound goes low and then comes back as if it is wanting to cut out but doesnt.

Hope someone can help and that post actually made sense lol
TIA
damo