Hi, thank you for contacting JustAnswer.com. My name is***** will do my best to provide the right answer to your question.
The rattling noise is either owing to
1. the hard drive being mounted loosely, perhaps
2. the hard drive mounting being rather resonant, or itself mounted loosely,
3. the hard drive might possibly be defective and about to fail.
*If* you could post a brief (several seconds) WAV or similar sound file, recording the rattling noise, or send it to me via Customer Support at JustAnswer.com (*****@******.***), I could listen to it and judge more surely as to which of these problems might be the case, or whether it doubtfully is 4. quite normal enough.
Does this answer your question adequately yet? let me know, please.