New clunking sound upon startup

I have a MacBookPro6,1 running OS 10.6.8. For the past week I've heard some whirring and clunking when I start it up. I've checked a few forums and the blame was placed on the DVD unit. However, the clunking definitely seems to come from the left of the computer (as I face it) and the CD slot is on the right.

I really hope the problem isn't my hard drive, but what else could it be? I don't want to replace this computer for two reasons:

1. I've heard that Apple isn't currently making a 17" model

2. I can't upgrade my operating system because nothing newer than 10.6.8 is compatable with Scrivener, my most important software application.