Not to scare you or anything, but I suggest you backup all your important data as soon as you can. Recently, I bought a Hitachi Deskstar 7K250 160GB SATA drive for my PC, and I experienced similar noises comming from my hard drive.
I ran the hard drive for roughly 2 months, occasionally hearing a 'creaking' or 'crying' noise, even though it was brand new.
Anyway, after 2 months the hard drive failed on me. I found that Windows no longer loaded up properly, even after I reinstalled the OS. The hard drive is now useless.
Hitachi (formerly IBM) have had a bad reputation for hard drive reliability (the 'DeathStar'), and the current series of hard drives were supposed to change all that.
I'm not certain if what happened to my hard drive is the same thing that yours is going through. Just to be on the safe side though, get the drive checked out. Hard drives shouldn't make any serious noises, especially when brand new.
I have a couple of "deathstars" that died, and were replaced, the replacement 60gb has been in my htpc for over a year now and has been making the creaking / crying noise for around 6 months. The only reason its still in the machine is I dont really care if it dies, as it just contains the os + dvd / multimedia playback software, that I can easily reinstall.
I've also had another 2 20gbs early model Deskstars that were out of warranty when they died.
Basically I wouldnt put anything you care about on there