I might be the only one to think this: I've fitted quite a few Maxtor 120Gb 7200rpm drives into Xbox's, and they are quite noisy/rough sounding? I have a Western Digital drive in my Xbox and it sounds totally different - quite quiet/smooth.
I have never had any problems with either make of drive, although I've never fitted a 5400rpm drive in an Xbox. (I'll need one soon though as my Sky+ will be getting upgraded, and I plan on using the drive Sky provide in their Sky+160 box).