Well, that grate leads to the hard drive. Air comes in through that grill, past the hard drive, into the heat sink, through the fan and out the hinge grill. If the grating noise is coming out of the hinge grill also, it is most likely that you need a replacement fan. If it is just coming from the front portside grill, then it would appear to be a hard drive problem. Generally however, hard drive problems cause the the computer to stop functioning. Can you still boot up your system, read files e.t.c?