Mine is also a Hitachi 5400. And I did actually have mine replaced by apple. They put in a brand new one (same brand) and there was no difference, which is why I don't think the drives are faulty, but it's rather an issue of the computer interacting with the drive.
I'm telling you this so you don't waste time replacing the drive.
FWIW, I installed the hdapm, and I think it's helping (the drive does seem much calmer, and thus a bit quieter. Not totally silent, perhaps, but not as noisy). It will take a couple of days to really know, but I think it's worth a try for anyone having this issue.
I would like to know, though, if there's a way to find out if it's installed correctly and if it's actually doing it's thing? It doesn't seem to show up in Activity Monitor...
This is absolutely an acoustics issue, and jomama has identified it. The Hitachi drive has platters that are always circling (that's the whirring sound you're all hearing). It gets quieter when you put your hand on top of the right palm rest area because your hand dampens the sound that's coming through that thin piece of aluminum between the hard drive and the top of the case. There's nothing you can do about this short of
A: getting a new brand of hard drive that might have a quieter idle speed or getting a SSD drive.
B: figure out what kind of rubber heat resistant dampening material you can apply to the inside of the macbook pro where the bottom of the hard drive meets the aluminum case.
This isn't a faulty drive issue. The Hitachi's are slightly louder than other drives apparently, and the design of the new ultra thin macbook pros allows more sound to come through the top of the case where the hard drive rests. It is kind of annoying to have to listen to the high pitched whirring sound in very quiet environments, but replacing the drive with another apple branded hitachi will not do any good. They will sound identical because of the acoustic properties in the unibody. Everyone who has a unibody macbook pro regardless of their hard drive brand/speed can make the whirring sound quieter by pushing their hand on top of the right palm rest area. This is confirmation that what you're hearing is the NORMAL sound of the HD resonating through the aluminum case. It sucks that there isn't more dampening there, and I'm personally trying to find some material to help reduce the noise. Unless you switch to a SSD drive, you will hear this whirring sound in quiet environments no matter what. Please try the steps I've mentioned above to make sure that you're hearing the hard drive and not having a faulty fan issue which sounds like a constant clicking in the upper left or right hand corners of the keyboard. These are separate sounds/issues.
The other complaint in this thread is a seemingly random single click that the hard drive makes every 5 to 20 seconds when idle. THIS IS ALSO COMPLETELY NORMAL BEHAVIOR. Do not assume your hard drive is breaking. Mac OS has an aggressive hard drive head parking command that makes your drive park its heads frequently to avoid data loss and save power. If you can't deal with this noise, then please do try the hdapm software mentioned previously in this thread. I hope that clears some of this up. I am by no means an expert, but I've gleaned all this info from other threads and the 3 separate macbook pro's I've been using for the last three months.
EDIT: I'm going to try some rubber grommets between the inside of the right palm rest area and the hard disk. These grommets should isolate the drive from the chassis and hopefully reduce the noise that's transmitted through the aluminum body of the mbp.
