High HD temp, what's going on?

[seiyafan]

I had the side cover removed with the case laying on its side since I started building it. Now the temperature of HD (it's SMART HD in MBM) says 45C. I have Prime running on it to stress test the CPU and RAM, ironically the CPU temp tops out at 38C, HD seems idle all the time during Prime test. The surface of HD definitely feels warm when I touch it. My HD is Seagate 7200.7 160GB, it's very quiet and it should be cool. Any idea?