My new mac pro is making a mysterious "eerrrrrrr" noise. It is weird because it was making it and than all of a sudden my wife's cat whacked into it and it stopped. Then the stupid cat whacked into it again and it started again! I did just install a new hard-drive and memory but I was pretty careful with both having done it before. The hard-drive seems secure, could the noise be the fact that the hard-drive might just need to be tightened some? Any other thoughts?