The way mac designs their notebooks is one of genius and of shear, unbridled schizophrenia, so yes, there are many, many, important screws inside the mac, many of which are very, very, small and can easily be forgotten.
However, if it was a power issue, that would mean the drive was not plugged in properly when you bought it from the store, so when they “fixed it” they would have plugged it in all the way (or something similar) as far as the case being lose, all I can say is they must have forgotten some padding or some screws.
The drive should be loud, not to the point you need to yell over it, but to the point that people at a crowed bus stop would know you are burning a DVD, (get what I mean?) Mainly because those super drives spin wicked fast to burn DVD’s.
I would say if it feels like the case could bend or brake, or in some other way cause massive damage to the notebook, I would take it to the closest Apple Store and ask the Geniuses there to take it apart and see if Mac forgot to put something back in.
The other option, if you are feeling adventurous, is shim the metal with a piece of cardboard as I have had to do for many of my friends using Black and White MacBooks. It may not be pretty but it works.