I have the exact same problem with my new dell inspiron 1520... not very impressed. Its sounds like the old computer i used to have about 5 years ago!!
Whenever it is 'thinking' it makes this incredibly annoying creaking or ticking noise. Even when there are no processes running it is still doing it.
It also makes this other random noise when it is just sitting there which I wouldn't know how to describe..
Dell are sending out someone to replace the hard drive for me, but if this doesn't fix the problem I'm sending it back under the 15 day total satisfaction policy!
I didn't pay $1600 for a creaking laptop that drives me mad when I'm trying to study