Hey, Lately my 27" late 2009 iMac (Quad Core i5) started randomly freezing completely (The entire OS froze without a kernel panic. Pressing the power button for a few seconds was required to shut it down). So far it happened 4 times. In 3 of the times, the bottom right area of the Mac, where the HDD is located, started clicking in a loop as soon as it froze. In the 4th time, I wasn't near by when it happened, so it might have made these noises and eventually stop. Since one week before the first time it happened I upgraded the RAM, my first suspect was faulty RAM. I booted to Memtest86+ and let it run, and it did find a one bit error almost 9GB into the the address space. I let it run later again for 8 and a half hours, and it found the same bit again, but only once. (Screenshots of Memtest86+ show that if the same bit fails again, it should be listed again. I found it very weird it only failed once in 8 hours, yet it popped relatively early both times I ran it) However, problems caused by faulty RAM are usually non-deterministic, yet the problem I'm having is the same every time freezing with HDD clicks. Did anyone ever have this problem before? Could the HDD be defective too? Thanks!