I just bought a Seagate 80GB SATA HD(ST380013AS)
,after 2 days using it, I find the new HD has a noise ,its not very loud but the noise is obvious louder than my old WD 80 7200rmp HD, so is it normal? should I take it back and change it?
Could just be a loud ground strap (the thing that rubs on the platter/spindle to get rid of the static charges). Could just be that it needs to be lubricated or something, but I wouldn't have the foggiest idea how to do that and I wouldn't suggest that you do it yourself.
Seagate drives seem to vibrate more than others. If you have a steel case, perhaps the vibrations are reverberating off structures inside the case. Try tightening the screws that hold the drive in. Sometimes they loosen which may create the noise.
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