The small office where I recently started working provided me with a new Dell Inspiron 570 for my office.  I am happy with it in every way that I could possibly be happy with a desktop, except for one thing.  It is absolutely silent for the first little while after it boots up, then I hear a slowly increasing buzzing noise, which becomes quite loud.  I have a couple of heavy books sitting on top of the unit, which stifles the noise temporarily, but after a few minutes it starts buzzing again.  I shift the books, which silences the buzzing, until a few minutes later it...STARTS BUZZING AGAIN.  It's driving me nuts.  I searched for anyone else having similar problems, and found a 2008 thread about the XPS 420, but couldn't find any solutions there.  

Is anyone else having this issue, and more importantly, HOW DID YOU FIX IT???

Thanks!