I have just returned iMac from service. I have installed new HDD in it and when I start iMac everything is fine for a few minutes but then fan start to become noisy and noisy and noisy... This is my stats: ODD: 998 RPM HDD:4358 RPM CPU:1199 RPM Is this values normal or I should worry about it? Noise is very loud. I have tried to unplug power cable for 15sec and after 5 sec to turn mac on doesn't help.