I've just bought a new laptop but whenever I turn off the computer, after the hard drive's heads would have retracted and as the platters begin to spin down, I hear a faint grinding noise that decreases in pitch as the platters slow. Under all other conditions it's as quiet as normal.
I'm figuring this is probably a bad bearing in the assembly, especially as an identical laptop with an identical hard drive model doesn't make the same noise under the same conditions. Am I right or completely off base? I presume I'm going to have a hard drive that's going to fail prematurely and suddenly.
I would say you are at least on the right general track, with as much certainty as you can have without actually inspecting the bearings. And if it is a bearing, then there's no saying when it will fail. Sometimes you can have a bearing that makes an unholy level of noise for years, meanwhile a "normal" drive might fail out of nowhere. However, the odds of the drive failing sooner rather than later are always higher if you're hearing abnormal noise, so since it's a new laptop either exchange it for a new one or submit a warranty claim to get the drive replaced.
I agree with Scott. If you are hearing unusual noises from a new HDD, it's not going to improve with time. You could check it with one of the HDD analysis programs, like HD Tune Pro, but in the end you are not going to feel good about the drive, and always wonder when it's going to fail you.
Since it's new, exchange it for a new one. I don't like purchasing a new item of any kind, then having to warranty repair it, when it should be "new" in the first place.