Well, feel such a (insert appropriate swear word here)! Unplugged all drives etc and powered on one at a time to see if I could hear where the noise was coming from. After about 10 mins I thought it sounded like it was coming from my front bottom fan on my Antec 1200 case. Checked that no cables etc were hitting the fan and all clear. Removed the fust filter and.....SILENCE. When I checked the filter there is a sliver of plastic hanging off that must have been hitting the fan. What really threw me was the hard drive led was always on when it was noisy and it's only just happened tonight.
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