Frequent crashing and unresponsive OS X
Interesting.  I have a ST9500420AS, is it the same drive?  Mine is loud but I don't have any issues with it.

Does anything show up in the console during/after this occurs?  /Applications/Utilities/Console.app

Also, if you can make the problem re-produceable, you could try fseventerhttp://www.fernlightning.com/doku.php?id=software:fseventer:start, or even a simple command into the terminal (lsof &gt; ~/Desktop/open_files.txt) to figure out what might be going on.

It almost sounds like it might, might be a hardware problem rather than software, but we may as well rule out the latter first.