Intermittent buzzing sound on Acer Aspire 5750

Hi,

I have had my Acer Aspire 5750 for 11 months and pretty much since day 1 there has been an intermittent buzzing sound occur, on average, every 5 minutes. I would point out that the buzzing sound only occurs if you playing something that has sound, e.g. a CD, a YouTube clip, a video file. The majority of the time I am using the laptop for excel, word, web browsing and email and, as none of these things contain sound, the laptop works perfectly well with no issues. When I play something with sound, I will hear a short buzzing sound lasting approximately 2 seconds and then everything will continue as normal for another 5 minutes, approximately, until the next buzzing sound. The problem is not any better or worse than when I first got the laptop but I'm at a stage where I would like to play more music on my laptop but currently with this buzzing sound, it is too annoying to do so. If I am playing a video file then, at the point that the buzzing occurs, the picture will also stutter but then continue as normal once the buzzing sound has stopped.